Method of manufacturing light emitting device

ABSTRACT

A method of manufacturing a light emitting device can be provided. The method includes: providing a package having side walls which define a recess; disposing a light emitting element in the recess; injecting a sealing material in the recess of the package, sedimenting centrifugally the fluorescent material particles toward a bottom surface in the recess to form a sealing member that comprises a first sealing member portion and a second sealing member portion; and curing the binder to form a cured sealing member. The sealing material includes a binder and fluorescent material particles that includes particles of fluoride fluorescent material that have a composition including tetravalent manganese ions, at least one selecting from the group consisting of alkali metal elements and NH 4   +  and at least one selecting from the group consisting of Group 4 elements and Group 14 elements. The first sealing member portion covers the light emitting element, and includes a first binder portion and the fluorescent material particles located in the first binder portion. The second sealing member portion covers the first sealing portion, and includes a second binder portion and substantially no fluorescent material particles located in the second binder portion. The particles of fluoride fluorescent material include a surface region and an inner region, both the surface region and the inner region comprising tetravalent manganese ions. A tetravalent manganese ion concentration of the surface region of the particles of fluoride fluorescent material is lower than a tetravalent manganese ion concentration of the inner region of the particles of fluoride fluorescent material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of U.S.application Ser. No. 14/657,676, filed Mar. 13, 2015, and claimspriority under 35 USC 119 from Japanese patent Application No.2014-052797, filed Mar. 14, 2014 and Japanese Patent Application No.2015-047606, filed Mar. 10, 2015, the entire disclosures of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a method of manufacturing a lightemitting device.

2. Description of the Related Art

A light emitting diodes (LEDs) is a semiconductor light emitting elementproduced from a metal compound such as gallium nitride (GaN). Combiningsuch a semiconductor light emitting element and a fluorescent material,various light emitting devices to emit light of a while color, anincandescent lamp color, an orange color and so on have been developed.Those light emitting devices to emit a white light and so on can beobtained based on the principle of light-color mixing. As for the systemto emit a white light, there are well-known systems such as a systemwhich employs an ultraviolet-light emitting element and three types offluorescent materials which emit lights of a red (R) color, green (G)color, and blue (B) color, respectively, and a system which employs ablue-light emitting element and a yellow-light emitting fluorescentmaterial. Light emitting devices of the type which employ a blue-lightemitting element and a fluorescent material to emit yellow light etc.,are in demand in a wide range of fields such as general lighting,on-vehicle lighting, displays, backlights for liquid crystal devices. Ofthose, for the fluorescent materials used for a backlight of liquidcrystal device, in order to reproduce a wide range of colors on achromaticity diagram, high color purity is also demanded along with thelight emitting efficiency. Particularly, the fluorescent materials usedfor backlights for liquid crystal devices are required to havecompatibility in combination with a color filter, and for which, afluorescent material with a narrow half width of the emission peak hasbeen in demand.

Examples of known red fluorescent materials which have an excitationband in blue-color region and a narrow half width of the emission peakinclude fluoride fluorescent materials with compositions of:

K₂AlF₅:Mn⁴⁺, K₃AlF₆:Mn⁴⁺, K₃GaF₆:Mn⁴⁺, Zn₂AlF₇:Mn⁴⁺, KIn₂F₇:Mn⁴⁺,K₂SiF₆:Mn⁴⁺, K₂TiF₆:Mn⁴⁺, K₃ZrF₇:Mn⁴⁺, Ba_(0.65)Zr_(0.35)F_(2.70):Mn⁴⁺,BaTiF₆:Mn⁴⁺, K₂SnF₆:Mn⁴⁺, Na₂TiF₆:Mn⁴⁺, Na₂ZrF₆:Mn⁴⁺, KRbTiF₆:Mn⁴⁺, andK₂Si_(0.5)Ge_(0.5)F₆:Mn⁴⁺ (for example, see JP 2009-528429A).

Generally, in light emitting devices, in order to protect the lightemitting element, the light emitting element together with the bondedwires and other electrically conductive members is sealed with a sealingmaterial which contains a fluorescent material.

SUMMARY OF THE INVENTION

A method of manufacturing a light emitting device in which reduction inthe optical output and occurrence of deviation in chromaticity can besuppressed. The method includes: providing a package having side wallswhich define a recess; disposing a light emitting element in the recess;injecting a sealing material in the recess of the package, sedimentingcentrifugally the fluorescent material particles toward a bottom surfacein the recess to form a sealing member that comprises a first sealingmember portion and a second sealing member portion; and curing thebinder to form a cured sealing member. The sealing material includes abinder and fluorescent material particles that includes particles offluoride fluorescent material that have a composition includingtetravalent manganese ions, at least one selecting from the groupconsisting of alkali metal elements and NH₄ ⁺ and at least one selectingfrom the group consisting of Group 4 elements and Group 14 elements. Thefirst sealing member portion covers the light emitting element, andincludes a first binder portion and the fluorescent material particleslocated in the first binder portion. The second sealing member portioncovers the first sealing portion, and includes a second binder portionand substantially no fluorescent material particles located in thesecond binder portion. The particles of fluoride fluorescent materialinclude a surface region and an inner region, both the surface regionand the inner region comprising tetravalent manganese ions. Atetravalent manganese ion concentration of the surface region of theparticles of fluoride fluorescent material is lower than a tetravalentmanganese ion concentration of the inner region of the particles offluoride fluorescent material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of lightemitting device according to an embodiment.

FIG. 2 is a diagram showing a fluorescent microscope image of anenlarged cross section of a light emitting device according to anembodiment.

FIG. 3A is a diagram showing a PCT result of a light emitting deviceaccording to Example 1 for 200 hours

FIG. 3B is a diagram showing a PCT result of a light emitting deviceaccording to Comparative Example 1 for 4 hours

FIG. 3C is a diagram showing a PCT result of a light emitting deviceaccording to Comparative Example 1 for 100 hours

FIG. 3D is a diagram showing a PCT result of a light emitting deviceaccording to Comparative Example 1 for 200 hours

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fluoride fluorescent materials activated with Mn⁴⁺ which can emit redlight with a narrow half width of the emission peak are assumed to besuitable for the use in display devices, and practical use of suchfluoride fluorescent materials has been in demand. However, it isconsidered that in such conventional fluoride fluorescent materialsactivated with Mn⁴⁺, tetravalent manganese ions which are constituentcomponents of the fluoride fluorescent materials and present on thefluorescent material particles may react with atmospheric moisture togenerate manganese dioxide which darkens the surfaces of the particles,resulting in deviation in the chromaticity and reduction in the opticaloutput over time. For this reason, the conventional fluoride fluorescentmaterials activated with Mn⁴⁺ may be difficult to apply for thebacklight of liquid crystal display devices, which emphasizes thereliability.

Accordingly, an aim of the present disclosure is to provide a lightemitting device in which reduction in the optical output and occurrenceof deviation in chromaticity can be suppressed, and to provide a methodof manufacturing the light emitting device.

Specific examples for achieving the objects will be described below. Thepresent disclosure includes embodiments as described below. A lightemitting device according to a first aspect of the disclosure includes apackage having side walls which define a recess, a light emittingelement arranged in the recess, and a sealing member which seals thelight emitting element. The sealing member includes a first sealingmember portion which covers the light emitting element and contains afirst binder portion and fluorescent material particles located in thefirst binder portion, and a second sealing member portion which coversthe first sealing member portion and contains a second binder portionand substantially no fluorescent material particles located in thesecond binder portion. The fluorescent material particles includesparticles of fluoride fluorescent material that is activated withtetravalent manganese ions and has a composition including tetravalentmanganese ion, at least one selecting from the group consisting ofalkali metal elements and NH₄ ⁺, and at least one selecting from thegroup consisting of Group 4 elements and Group 14 elements. Theparticles of fluoride fluorescent material include a surface region andan inner region and both the surface region and the inner region containtetravalent manganese ions. A tetravalent manganese ion concentration ofthe surface region of the particles of fluoride fluorescent material islower than a tetravalent manganese ion concentration of the inner regionof the particles of fluoride fluorescent material.

A method of manufacturing a light emitting device according to a secondaspect of the disclosure includes providing a package having side wallswhich define a recess; disposing a light emitting element in the recess;injecting a sealing material in the recess of the package, the sealingmaterial including particles of a fluoride fluorescent material and abinder, the fluorescent material particles including particles offluoride fluorescent material that have a composition includingtetravalent manganese ion, at least one selecting from the groupconsisting of alkali metal elements and NH₄ ⁺, and at least oneselecting from the group consisting of Group 4 elements and Group 14elements; sedimenting centrifugally the fluorescent material particlestoward a bottom surface in the recess to form a sealing member thatincludes a first sealing member portion and a second sealing memberportion, the first sealing member portion covering the light emittingelement, and including a first binder portion and the fluorescentmaterial particles located in the first binder portion, and the secondsealing member portion covering the first sealing portion, and includinga second binder portion and substantially no fluorescent materialparticles located in the second binder portion; and curing the binder toform a cured sealing member, wherein the particles of fluoridefluorescent material include a surface region and an inner region, boththe surface region and the inner region including tetravalent manganeseions, and wherein a tetravalent manganese ion concentration of thesurface region of the particles of fluoride fluorescent material islower than a tetravalent manganese ion concentration of the inner regionof the particles of fluoride fluorescent material.

Accordingly, a light emitting device in which reduction in the opticaloutput and occurrence of deviation in chromaticity can be suppressed,and a method of manufacturing the light emitting device can be provided.

A light emitting device and a method of manufacturing the light emittingdevice according to the present disclosure will be described below byway of the embodiments. The embodiments are intended as illustrative ofa light emitting device and a method of manufacturing the light emittingdevice to give a concrete form to technical ideas of the presentinvention, and the scope of the invention is not limited to thosedescribed below. In the specification, the relation between the colornames and the chromaticity coordinates, the relation between the rangeof wavelength of light and the color name of single color light, and thelike conform to JIS Z8110. More specifically, the wavelengths of 380 nmto 410 nm correspond to purple light, 410 nm to 455 nm correspond toblue purple light, 455 nm to 485 nm correspond to blue light, 485 nm to495 nm correspond to blue green light, 495 nm to 548 nm correspond togreen light, 548 nm to 573 nm correspond to yellow green light, 573 nmto 584 nm correspond to yellow light, 584 nm to 610 nm correspond toyellow red light, and 610 nm to 780 nm correspond to red light.

In the specification, the term “step” refers not only an independentstep but also a step which is indistinguishable from other step butwhich can achieve an intended purpose. Also, a numerical range indicatedusing “to” in the present specification represents a range includingnumerical values described before and after “to” as a minimum value anda maximum value, respectively. Further, the “content of each componentin the sealing material” indicates that in the case where a pluralnumber of substances corresponding to each component are present in thesealing material, refers to a total amount of the plural number ofsubstance in the sealing material, unless otherwise stated.

Light Emitting Device

FIG. 1 is a diagram illustrating a light emitting device according to afirst embodiment. With referring to FIG. 1, the light emitting device 1according to the first embodiment will be described. A light emittingdevice 1 includes a package 3 having side walls which define a recess 2;a light emitting element 4 arranged on a bottom of the recess 2; andsealing members 9, 10 which seals the light emitting element 4. Thesealing members 9, 10 respectively include a first portion 9 whichcontains fluorescent material particles 7, 8 and covers the lightemitting element 4, and a second portion 10 which does not contain thefluorescent materials 7, 8 and is arranged over the first portion 9. Thefluorescent material particles 7 contains particles of a fluoridefluorescent material activated with tetravalent manganese and has acomposition including tetravalent manganese ion, at least one selectingfrom the group consisting of alkali metal elements and NH₄ ⁺, and atleast one selecting from the group consisting of Group 4 elements andGroup 14 elements. The fluoride fluorescent material has, for instance,a composition represented by the following formula (I). The fluorescentmaterial particles 7 have a surface region in which a tetravalentmanganese ion concentration is lower than a tetravalent manganese ionconcentration of an inner region of the fluorescent material particles7. The fluorescent material particles 8 are particles of a fluorescentmaterial other than the fluoride fluorescent material described above,hereinafter the fluorescent material particles may be referred to “otherfluorescent material particles”.

A₂[M_(1-b)Mn⁴⁺ _(b)F₆]  (I)

In the formula (I), A is at least one selecting from the groupconsisting of alkali metal elements and NH₄ ⁺, M is at least oneselected from the group consisting of Group 4 elements and Group 14elements, and 0<b<0.2.

As shown in FIG. 1, the light emitting device 1 includes a package 3having side walls which define a recess 2, a light emitting element 4arranged in the recess 2, and a first portion 9 which contains particlesof a fluoride fluorescent material 7, and other fluorescent materialparticles 8 and covers the light emitting element 4, and a secondportion 10 which substantially does not contain the fluorescent materialparticles and is arranged over the first portion 9. As described below,the first portion 9 and the second portion 10 can be formed by curingthe sealing material which contains at least a binder and a fluorescentmaterial.

The light emitting element 4 is arranged on a first lead 5 disposed onthe bottom of the recess 2 of the package 3. With its positive andnegative electrodes, the light emitting element 4 is connected to afirst lead 5 and a second lead 6 which are made of a metal and are fixedto the package 3 via wires 11, 12, respectively. The first lead 5 andthe second lead 6 constitute the bottom surface of the recess 2 of thepackage 3.

As shown in FIG. 1, the first portion 9 and the second portion 10 may bein a state in which a same binder which also serves as a sealing memberis contained and an interface between the first portion 9 and the secondportion 10 can be clearly distinguished, but is not limited thereto.

Package

The material of the package having side walls which define a recess isnot specifically limited and an electrically insulating material havinggood light resistance and heat resistance can be suitably used. Forexample, the package can be formed with a material such as a resin, aceramics, or the like. Examples of the resin used for the material ofthe package include, a thermoplastic resin such as a polyphthalamideresin, a thermosetting resin such as an epoxy resin, and a glass epoxyresin.

Light Emitting Element

A light emitting element which can emit a light of a short-wavelengthregion of visible light can be used. For example, a light emittingelement for emitting light of a blue color or a green color, anitride-based semiconductor (In_(X)Al_(Y)Ga_(1-X-Y)N, 0≦X, 0≦Y, X+Y≦1)etc., can be used. As a light source, hereinafter may be referred to asan “excitation light source”, a light emitting element which can emitlight whose emission peak wavelength being in a range of 380 nm to 485nm, of a short-wavelength region of visible light, can be preferablyused. A light source preferably has an emission peak wavelength (maximumemission wavelength) in a wavelength range of 420 nm to 485 nm, morepreferably in a wavelength range of 440 nm to 480 nm. With thisconfiguration, the fluorescent material can be efficiently excited, sothat the visible light can be effectively used. Also, with the use of alight source of the wavelength range as described above, a lightemitting device with high emission intensity can be obtained. With theuse of a semiconductor light emitting element as an excitation lightsource, a light emitting device which has high linearity of outputtingto inputting in high efficiency and exhibits high stability tomechanical impacts can be obtained.

First Lead and Second Lead

The first lead 5 and the second lead 6 are arranged at the bottom of therecess 2 of the package 3, and the first lead 5 and the second lead 6constitute the bottom surface of the recess 2 of the package 3. Thefirst lead and the second lead may be referred to collectively as“electrically conductive members” and individually as an “electricallyconductive member”. Each of the first lead 5 and the second lead 6 maybe made singly of an electrically conductive base material, or may bemade of a base member and includes a reflecting layer. Each of the firstlead 5 and the second lead 6 may be made singly of an electricallyconductive reflecting layer. Each of the first lead 5 and the secondlead 6 may be made of an electrically conductive base material and areflecting layer, with one or more other members being interposedtherebetween. In the case where the electrically conductive memberincludes a base material and a reflecting layer, the reflecting layer isarranged at a side where a light emitting element 4 to be mounted.

Base Material of First Lead and Second Lead

In the case where the base material of the first lead and the secondlead have electrically conducting property, for example, copper or acopper alloy may be used. Examples of other materials suitable for thebase material of the first lead and the second lead include a ceramicmaterial, an epoxy resin, a polyimide resin. The first lead and thesecond lead are approximately plate-like members which can mount a lightemitting element 4 and constitute the bottom surface of the recess 2 ofthe package 3. Alumina, aluminum nitride, mullite, silicon carbide,silicon nitride, or the like can be used as the ceramic material. Also,a base material may be a calcined stacked-layer of ceramic green sheets,which are obtained by mixing ceramic powder and a resin, forming themixture into a sheet shape, processing the green sheet into individualgreen sheets, and stacking the individual green sheets and calcining thestacked ceramics green sheet. A base material which employs an epoxyresin may be obtained by, for example, attaching a copper plate on aprepreg which is obtained by impregnating an epoxy resin into a glasscloth and semi-cured it, or on a semi-cured epoxy-resin, then applyingheat to effect thermosetting.

Reflecting Layer of First Lead and Second Lead

For the reflecting layer, for example, a material which contains silveror aluminum can be used, and particularly, a material which containssilver which has a high reflectance is preferably used. Examples of suchmaterials include metals such as copper, aluminum, gold, silver,tungsten, iron, nickel, iron-nickel alloy, phosphor bronze, iron copper,or the like.

Insulating Member

The light emitting element 4, the first lead 5, the second lead 6, andthe wires 11, 12 are preferably covered with an insulating member. Theinsulating member is preferably disposed continuously on the lightemitting element 4, the first lead 5, the second lead 6, and the wires11, 12. In the specification, the expression “disposed continuously”includes a state of the insulating member being disposed in the form ofa layer (or film) on the object which is made up of the light emittingelement 4, the first lead 5, the second lead 6, and the wires 11, 12, ora state in which, while leaving partially uncovered spots, power-shapeor needle-shaped insulating member is applied on approximately whole ofthe light emitting element 4, the first lead 5, the second lead 6, andthe wires 11, 12. The insulating member can block the gas, moisture, andfluorine (F) contained in the fluorescent material which may deterioratethe metals which constitute the light emitting element 4, the first lead5, the second lead 6, and the wires 11, 12, in particular, silver whichconstitutes the first lead 5 and the second lead 6. The fluorinecontained in the fluorescent material and the silver contained in theelectrically conductive members or the like may react to generate silverfluoride having a dark color, which may absorb light emitted from thelight emitting element, resulting in a reduction of optical output.Deterioration of silver contained in the first lead 5, the second lead6, or the like can be efficiently suppressed by the insulating member,so that the light output efficiency can be improved. The insulatingmember can serve as a passivation layer which can block gases such assulfur (S) and oxygen (O), moisture, and fluorine (F) etc., contained inthe fluorescent material, so that migration of silver contained in thefirst lead 5, the second lead 6, etc., can be suppressed.

Material of the insulating member preferably has light-transmissiveproperty, and an inorganic material is preferably employed. Examples ofthe material for the insulating member include oxides such as SiO₂,Al₂O₃, TiO₂, ZrO₂, ZnO₂, Nb₂O₃, MgO, SrO, In₂O₃, TaO₂, HfO, SeO, Y₂O₃,nitrides such as SiN, AlN, AlON, fluorides such as MgF₂. Those materialsmay be used singly or in combination of two or more kinds.Alternatively, two or more layers of insulating members which containone or two or more materials may be stacked.

The insulating member preferably has a thickness which does not allowoptical loss due to multiple reflection at each of the interfacesbetween the electrically conductive member, the insulating member, thefirst portion 9, the second portion 10, or the like. Meanwhile, theinsulating member is required to have a thickness sufficient forblocking a gas and moisture, and fluorine (F) or the like contained inthe fluorescent material so as to prevent a reaction between theelectrically conductive member and a gas and moisture, and fluorine (F)or the like contained in the fluorescent material. The thickness of theinsulating member may be varied slightly according to the material orthe like of each member which constitutes the light emitting device. Theinsulating member preferably has a thickness of about 1 nm to about 100nm. The insulating member more preferably has a thickness of 1 nm to 50nm, further preferably 2 nm to 25 nm, and particularly preferably 3 nmto 10 nm.

It is preferable that the insulating member is made of an inorganiccompound disposed in a form of a film (e.g. a layer) disposed on theelectrically conductive member, the wires 11, 12, and the light emittingelement 4, by using sputtering, vapor deposition, or the like. It ismore preferable that the insulating member is formed by using atomiclayer deposition method. Atomic layer deposition method is a method forforming layers of a reactive component one atomic layer at a time.Different from an conventional method such as sputtering or vapordeposition, in an atomic layer deposition method, a reactive componentcan be uniformly supplied on the target even in the presence of anobstacle, so that a high quality protective layer with uniform thicknessand uniform composition can be formed. The insulating member (e.g. afilm) formed by using atomic layer deposition method has a smallthickness, so that absorption of light by the insulating member can bereduced, and thus a light emitting device with can exhibit high opticaloutput in its initial characteristics can be provided.

Next, an example of forming an insulating member (e.g. a film) ofaluminum oxide (Al₂O₃) by using atomic layer deposition method will bedescribed. First, trimethylaluminium, hereinafter may be referred to as“TMA”, gas is introduces to the surface of the target materials of theelectrically conductive member, the wires 11, 12, and the light emittingelement 4 so that the OH groups in the electrically conductive member,the wires 11, 12, and the light emitting element 4 are allowed to reactwith the TMS gas (first reaction). Next, excess gas is evacuated. Then,H₂O gas is introduced to the target materials so that the TMA reactedwith the OH groups in the first reaction is allowed to react with theH₂O (second reaction). Next, excess gas is evacuated. The firstreaction, evacuation, the second reaction, and evacuation are taken asone cycle and the cycle is repeated a plurality of times. Thus, a filmof aluminum oxide (Al₂O₃) of a desired thickness is formed on theelectrically conductive member, the wires 11, 12, and the light emittingelement 4.

First Portion and Second Portion

A first portion 9 and a second portion 10 constitute a sealing memberfor sealing the light emitting element 4. The first portion 9 and thesecond portion 10 can be formed by using a sealing material whichcontains at least a binder and a fluorescent material. The sealingmaterial is injected in the recess 2 of the package 3 where the lightemitting element has been arranged 4. The fluoride fluorescent materialparticles 7 and other fluorescent material particles 8 contained in thesealing material are centrifugally sedimented to the light emittingelement 4 side, then, the binder is cured. Thus, the first portion 9which covers the light emitting element 4 and contains the fluoridefluorescent material particles 7 and other fluorescent materialparticles 8 and the second portion 10 which substantially does notcontain the fluoride fluorescent material particles 7 and otherfluorescent material particles 8 are formed.

The first portion 9 contains the fluoride fluorescent material particleswhich have a chemical composition represented by the formula (I), andthe particles have a surface region which has tetravalent manganese ionconcentration lower than the tetravalent manganese ion concentration inan inner region. In the sealing material which contains at least abinder and a fluorescent material including the fluoride fluorescentmaterial particles, the fluoride fluorescent material particles aresufficiently dispersed so that by centrifugal separation, thefluorescent material particles are sedimented on the light emittingelement without over packing and the sealing material is layer-separatedto obtain the first portion 9 and the second portion 10 before curing.

The first portion 9 and the second portion 10 contain a common binderwhich allows for suppression of deterioration in the optical output ofthe light emitting element and chromaticity deviation. The lightemitting element 4 is covered with the fluorescent material particles 7and other fluorescent material particles 8, so that the wavelength ofthe light emitted from the light emitting element can be efficientlyconverted by the fluorescent materials and the light can be efficientlyemitted.

However, it is considered that in such a conventional fluoridefluorescent materials activated with Mn⁴⁺, tetravalent manganese ionswhich are constituent components of the fluoride fluorescent materialand present on the fluorescent material particles may react withmoisture in the air to generate manganese dioxide which darkens thesurfaces of the particles, resulting in occurrence of deviation in thechromaticity and reduction in the optical output. On the other hand, inthe light emitting device according to an embodiment, entering of theatmospheric moisture from the interface between the light emittingsurface created by the second portion 10 and the package 3 can beblocked by the second portion 10. Blocked by the second portion 10, themoisture in the air hardly reach the fluorescent material particles 7and other fluorescent material particles 8 contained in the firstportion 9, so that reaction between the moisture and the tetravalentmanganese ions contained in the fluoride fluorescent material activatedwith Mn⁴⁺ in the first portion 9 can be prevented, and thus generationof manganese dioxide which darkens the surfaces of the particles can beprevented. Accordingly, deterioration in the optical output anddeviation in the chromaticity can be suppressed in the light emittingdevice according to the present embodiment and sufficient durability canbe achieved in a long-term reliability test. Moreover, in the lightemitting device according to the present embodiment, by the secondportion 10, the moisture in the air can be blocked from reaching thefluoride fluorescent material contained in the first portion 9, so thatdeterioration of the fluoride fluorescent material can be suppressed.When the fluoride fluorescent material deteriorates, Mn⁴⁺, F⁻, or thelike contained in the fluoride fluorescent material may be eluted,resulting in a deterioration of the binder which constitutes the firstportion 9 and the second portion 10. But according to the presentembodiment, deterioration of the fluoride fluorescent material can beprevented, and which further allows to prevent deterioration of thefirst portion 9 and the second portion 10.

The second portion preferably has a thickness of one tenth or greaterwith respect to the entire thickness of the sealing member, at directlyabove the light emitting element. With the thickness of the secondportion directly above the light emitting element one tenth or greaterwith respect to the entire thickness of the sealing member, theconverted light by the fluorescent material can be efficiently releasedto the outside of the light emitting device.

The second portion preferably has a thickness of one fourth or greaterwith respect to the entire thickness of the sealing member, at directlyabove the light emitting element. With the thickness of the secondportion directly above the light emitting element one fourth or greaterwith respect to the entire thickness of the sealing member, the moisturein the air can be blocked by the second portion 10, so that the moisturehardly reach the fluorescent materials contained in the first portion,so that reaction between the moisture and the tetravalent manganese ionscontained in the fluoride fluorescent material activated with Mn⁴⁺ inthe first portion 9 can be prevented, and thus generation of manganesedioxide which darkens the surfaces of the particles can be prevented.

Sealing Material

The sealing member including the first portion and the second portioncan be formed with a sealing material which contains at least a binderand a fluorescent material and which becomes the sealing member uponbeing cured. The sealing material which constitutes the sealing memberthrough curing may further contain a filler material which has a volumeaverage particle size of 1 μm to 20 μm. The sealing material may furthercontain a nano-filler material which has a primary particle with anaverage particle size of 5 nm to 20 nm.

Binder

The binder contained in the sealing material which constituted thesealing member preferably has light-transmissive property allowing lightfrom the light emitting element to pass through. Examples of the binderinclude a glass and a resin. The binder is preferably a resin. Specificexamples of the resin include a silicone resin, a modified siliconeresin, an epoxy resin, a modified epoxy resin, and an acrylic resin. Theresin is preferably at least one selected from the group consisting of asilicone resin, a modified silicone resin, an epoxy resin, a modifiedepoxy resin, and an acrylic resin. The resin may be a silicone resin, anepoxy resin, a urea resin, a fluororesin or a combination thereof. Amongthose, a modified silicone resin is preferably used, and a phenylsilicone resin in which a phenyl group is introduced in a part of thepolysiloxane side chains is preferable.

In the case where the binder in the sealing material is made of a resin,the content of the resin in the sealing material is preferably 5 to 95mass % with respect to 100 mass % of the sealing material. The contentof the resin in the sealing material with respect to 100 mass % of thesealing material is more preferably 35 to 85 mass %, further preferably40 to 80 mass %, and particularly preferably 45 to 75 mass %. In thecase where the binder in the sealing material is made of a resin, withthe content of the resin of 5 to 95 mass % with respect to 100 mass % ofthe sealing material, the members such as a light emitting elementarranged in the recess can be stably protected by the sealing memberwhich is formed by curing the sealing material. In addition, with thecontent of the resin in the sealing material in the range as describedabove, a sufficient amount of the fluorescent material to cover thelight emitting element can be contained in the first portion.

Fluoride Fluorescent Material

The fluorescent material contains particles of a fluoride fluorescentmaterial which is activated with tetravalent manganese ion and has acomposition including tetravalent manganese ion, at least one selectingfrom the group consisting of alkali metal elements and NH₄ ⁺, and atleast one selecting from the group consisting of Group 4 elements andGroup 14 elements and the particles have a surface region in which atetravalent manganese ion concentration is lower than the tetravalentmanganese ion concentration in the inner region. That is, the particlesof fluoride fluorescent material include a surface region and an innerregion, and a tetravalent manganese ion concentration of the surfaceregion is lower than a tetravalent manganese ion concentration of theinner region. The particles of fluoride fluorescent material have, forinstance, a composition represented by the formula (I).

A₂[M_(1-b)Mn⁴⁺ _(b)F₆]  (I)

In the formula (I), A is at least one selected from the group consistingof alkali metal elements and NH₄ ⁺, or A is a cation which contains atleast K⁺ and may further contain at least one selected from the groupconsisting of Li⁺, Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺, M is at least one selectedfrom the group consisting of Group 4 elements and Group 14 elements, and0<b<0.2.

The fluoride fluorescent material which has a chemical compositionrepresented by the formula (I) and the particles thereof have a surfaceregion in which a tetravalent manganese ion concentration is lower thanthe tetravalent manganese ion concentration in the inner region is a redlight-emitting fluorescent material with a narrow half value width ofthe emission spectrum and has excellent water resistance and the lightemitting device according to an embodiment can exhibit satisfactorydurability in a long-term reliability test. This can be considered asbelow, for example. However, it is considered that in such conventionalfluoride fluorescent materials activated with Mn⁴⁺, tetravalentmanganese ions which are constituent components of the fluoridefluorescent materials and present on the fluorescent material particlesmay react with moisture in the air to generate manganese dioxide whichdarkens the surfaces of the particles, resulting in occurrence ofdeviation in the chromaticity and reduction in the optical output overtime. Accordingly, satisfactory durability cannot be obtained in along-term reliability test, so that the usage which requiresreliability, for example, in-vehicle applications, has been regardeddifficult to implement. However, in the fluoride fluorescent materialsaccording to an embodiment of the present invention, the tetravalentmanganese ion concentration in the surface regions of the fluorideparticles is kept lower than the concentration in the inner regions.Accordingly, it is considered that generation of manganese dioxide onthe surfaces of the particles can be suppressed and deterioration in theoptical output and deviation in the chromaticity can be suppressed for along period. It is considered that, thus, good long-term reliability canbe achieved.

The particle diameter and the particle size distribution of the fluoridefluorescent material which has a chemical composition represented by theformula (I) are not specifically limited, but in view of the emissionintensity and durability, a particle size distribution with a singlepeak is preferable and a narrow particle size distribution with a singlepeak is more preferable. The surface area and the bulk density of thefluoride fluorescent material are not specifically limited.

The fluoride fluorescent materials are fluorescent materials activatedwith Mn⁴⁺ which can absorb light in a short-wavelength region and emitlight of red color. The excitation light which is a visible light in ashort wavelength region is preferably light in blue color region. Morespecifically, the excitation light preferably has a main peak wavelengthin an intensity spectrum in a range of 380 nm to 500 nm, more preferablyin a range of 380 nm to 485 nm, further preferably in a range of 400 nmto 485 nm, and particularly preferably in a range of 440 nm to 480 nm.

The emission wavelengths of the fluoride fluorescent materials are notspecifically limited as long as the emission wavelength is longer thanthe wavelength of its excitation light and in red color region. Theemission spectrum of the fluoride fluorescent material preferably has apeak wavelength in a range of 610 nm to 650 nm. The smaller half valuewidth of the emission spectrum is more preferable, and morespecifically, 10 nm or less is preferable.

In the formula (I), A is at least one selected from the group consistingof alkali metal elements and NH₄ ⁺, or A includes at least potassium ion(K⁺) and may further include at least one selected from the groupconsisting of lithium ion (Li⁺), sodium ion (Na⁺), rubidium ion (Rb⁺),cesium ion (Cs⁺), and ammonium ion (NH₄ ⁺). The content of potassium inA is not specifically limited, and for example, preferably 50 mole % orgreater and more preferably 80 mole % or greater.

In the formula (I), M is at least one selected from the group consistingof Group 4 elements and Group 14 elements. In view of luminouscharacteristics, M is preferably at least one selected from the groupconsisting of titanium (Ti), zirconium (Zr), hafnium (Hf), silicon (Si),germanium (Ge), and tin (Sn). More preferably, M includes silicone (Si)or silicone (Si) and germanium (Ge), and further preferably, M issilicone (Si) or silicone (Si) and germanium (Ge). In the case of Mincludes silicon (Si) or silicon (Si) and germanium (Ge), a portion ofat least one of Si and Ge may be substituted with at least one selectedfrom the group consisting of Group 4 elements including Ti, Zr, and Hf,and Group 14 elements including C and Sn. In such a case, the totalcontent of Si and Ge in M is not specifically limited and for example,50 mole % or greater is preferable and 80 mole % or greater is furtherpreferable.

The fluoride fluorescent material particles include an inner regionwhich is formed in a first step to be described in detail below and asurface region which is formed in a second step, a third step or avariant of the second step in which the concentration of tetravalentmanganese ion is lower than that in the inner region.

In the surface region of the fluoride fluorescent material particles,the concentration of tetravalent manganese ion is lower than that in theinner region. The surface region may be demarcated from the inner regionby a clear interface such as a two-layer structure, or the surfaceregion is not demarcated from the inner region by a clear interface andthe concentration of tetravalent manganese ion gradually decreases fromthe inner side of the surface region toward the outer side. Theparticles of the fluoride fluorescent material obtained by using amethod of manufacturing which is to be described below have a surfaceregion which do not have or have little amount of tetravalent manganeseions derived from tetravalent manganese ions, even when the surfaces ofthe fluoride fluorescent materials are eluded due to the humidity, sothat generation of manganese dioxide derived from tetravalent manganeseions can be suppressed while maintaining property which allows widecolor reproduction range in the image display device, compared to alight emitting device which employs a conventional fluoride fluorescentmaterial whose entire particles are activated with tetravalent manganeseions. Accordingly, blackening of the surfaces of the fluoridefluorescent material particles can be suppressed and deterioration inthe emission intensity can be reduced.

The average concentration of tetravalent manganese ions in the surfaceregion of the fluoride fluorescent material particles is preferably 30mass % or less with respect to the average concentration of tetravalentmanganese ions in the inner region. Further, the concentration oftetravalent manganese ions in the surface region is preferably 25 mass %or less, more preferably 20 mass % or less, with respect to theconcentration of tetravalent manganese ions in the inner region.Meanwhile, the concentration of tetravalent manganese ions in thesurface region can be 0.5 mass % or more with respect to that of theinner region. As described above, with the concentration of tetravalentmanganese ions being made approximately zero, humidity resistivityincreases, but as the concentration of tetravalent manganese ion in thesurface regions decreases, the ratio of the regions which do notcontribute to emission increases in the surface regions of fluoridefluorescent material particles, resulting in a tendency of decrease inemission intensity.

Although depending on the particle diameter of the fluoride fluorescentmaterial, the thickness of the surface region is preferably about 1/10to about 1/50 with respect to the average particle diameter. Forexample, in the case where the fluoride material particles have anaverage particle diameter of 20 to 40 μm, the thickness of the surfaceregion may be 2 μm or less.

The fluoride fluorescent material can be prepared so that an elutionamount of tetravalent manganese ion in pure water which is one to fivetimes greater in mass than the mass of the fluoride fluorescentmaterials is, for example, in a range of 0.05 ppm to 3 ppm at 25° C. Theelution amount of tetravalent manganese ion under a condition describedabove is preferably in a range of 0.1 to 2.5 ppm and more preferably ina range of 0.2 to 2.0 ppm. This is because, although the lower theelution amount of tetravalent manganese ion the higher the waterresistance will be, the greater the ratio of surface area with a lowconcentration of tetravalent manganese ion will result in a degradationof emission intensity as described above. The elution amount ofmanganese ion can be measured by using a quantitative analysis throughICP emission analysis, in which the fluoride fluorescent materials areplaced in pure water which is one to five times, preferably three times,greater in mass than the mass of the fluoride fluorescent materials andagitated at 25° C. for 1 hour. Then, a reducing agent is added to eludemanganese ion into the solution, and a supernatant is collected tomeasure by a quantitative analysis through ICP emission analysis.

With the fluoride fluorescent materials of the configuration asdescribed above, reduction in the optical output and deviation in thechromaticity accompanied with discoloration due to generation ofmanganese dioxide caused by tetravalent manganese ion resulting from thefluoride fluorescent materials contacting water, can be suppressed, sothat the fluoride fluorescent materials with high moisture-resistancecan be realized.

The moisture-resistance of the fluoride fluorescent materials can beconfirmed by discoloration through a pressure cooker test (PCT).Otherwise, the moisture-resistance can be evaluated by, for example, anemission luminance maintenance rate of after a water-resistance test,which is a rate (%) of the emission luminance after the water-resistancetest with respect to the emission luminance before the water-resistancetest. The emission luminance maintenance rate after the water-resistancetest is preferably 85% or more, and more preferably 90% or more. Morespecifically, in the present specification, the water-resistance test isperformed by placing fluoride fluorescent materials in water of one tofive times, preferably three times, in mass of the fluoride fluorescentmaterial sand agitate it at 25° C. for 1 hour.

Method of Manufacturing Fluoride Fluorescent Material

A method of manufacturing a fluoride fluorescent material which has aspecific composition including tetravalent manganese ion, at least oneselecting from the group consisting of alkali metal elements and NH₄ ⁺,and at least one selecting from the group consisting of Group 4 elementsand Group 14 elements, or a composition, for instance, represented bythe formula (I), and has a surface region in which a tetravalentmanganese ion concentration is lower than a tetravalent manganese ionconcentration in an inner region, the method includes a first step offorming an inner region, hereinafter may be referred to as a “coreportion”, a second step and a third step of forming a surface region.

First Step

A method of manufacturing a fluoride fluorescent material may furtherinclude providing a fluoride which has the specific composition, forinstance, represented by the formula (I). The step of providing caninclude steps of manufacturing a fluoride fluorescent material which hasthe specific composition. The fluoride fluorescent material having thespecific composition can be manufactured such that in a solvent whichcontains hydrogen fluoride, first complex ions which include tetravalentmanganese ions, cations which at least include potassium ions (K⁺), andmay further include at least one selected from the group consisting oflithium ions (Li⁺), sodium ions (Na⁺), rubidium ions (Rb⁺), cesium ions(Cs⁺), and ammonium ions (NH₄ ⁺), and second complex ions which includeat least one selected from a group consisting of Group 4 elements andGroup 14 elements are brought in contact with each other.

The fluoride fluorescent material having the specific composition can bemanufactured by, for example, a method which includes a step of mixing asolution a which at least contains a first complex ion which includestetravalent manganese ions, a second complex ion which includes at leastone selected from the group consisting of Group 4 elements and Group 14elements, and fluorine ion, and a solution b which at least contains K⁺,and may further contain at least one selected from the group consistingof Li⁺, Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺. Hereinafter, the step may be called asa “first step of manufacturing fluoride fluorescent material”.

Solution a

The solution a is a solution of a hydrofluoric acid which contains afirst complex ion which includes tetravalent manganese ions, and asecond complex ion which includes at least one selected from Group 4elements and Group 14 elements in addition to fluorine ions.

The manganese source for producing the first complex ion which includestetravalent manganese ion is not specifically limited as ion as it is achemical compound which contains manganese. Specific examples of themanganese source which can constitute the solution a include K₂MnF₆,KMnO₄, and K₂MnCl₆. Among those, K₂MnF₆ is preferable, because it can bepresent stably as a MnF₆ complex ion in hydrofluoric acid whilemaintaining the oxidation number (tetravalent) necessary for activating.Among the manganese sources, a manganese source which at least containspotassium ion (K⁺) and may further include at least one cation selectedfrom the group consisting of lithium ion (Li⁺), sodium ion (Na⁺),rubidium ion (Rb⁺), cesium ion (Cs⁺), and ammonium ion (NH₄ ⁺) can alsoserve as a cation source in the solution b. Those manganese sources forproducing the first complex ion may be used singly or in combination oftwo or more kinds.

The concentration of the first complex ion in the solution a is notspecifically limited. The lower-limit value of the first complex ionconcentration in the solution a is generally 0.01 mass % or greater,preferably 0.03 mass % or greater, and more preferably 0.05 mass % orgreater. The upper-limit value of the first complex ion concentration inthe solution a is generally 50 mass % or less, preferably 40 mass % orless, and more preferably 30 mass % or less.

The second complex ion preferably includes at least one selected fromthe group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf),silicon (Si), germanium (Ge), and tin (Sn), more preferably includessilicon (Si) or silicon (Si) and germanium (Ge), and further preferably,the second complex ion is a silicon fluoride complex ion. For example,in the case of the second complex ion includes silicon (Si), the secondcomplex ion source is preferably a chemical compound which containssilicon and fluorine and has high solubility in the solution. Specificexamples of the second complex ion source include H₂SiF₆, Na₂SiF₆,(NH₄)₂SiF₆, Rb₂SiF₆, and Cs₂SiF₆. Among those, H₂SiF₆ is preferablebecause of its high water-solubility and it's free from impurities ofalkaline metal elements. The second complex ion sources may be usedsingly or in combination of two or more kinds.

The lower-limit value of the second complex ion concentration in thesolution a is generally 5 mass % or greater, preferably 10 mass % orgreater, and more preferably 15 mass % or greater. The upper-limit valueof the second complex ion concentration in the solution a is generally80 mass % or less, preferably 70 mass % or less, and more preferably 60mass % or less.

The lower-limit value of hydrogen fluoride concentration in the solutiona is generally 20 mass % or greater, preferably 25 mass % or greater,and more preferably 30 mass % or greater. The upper-limit value ofhydrogen fluoride concentration in the solution a is generally 80 mass %or less, preferably 75 mass % or less, more preferably 70 mass % orless.

Solution b

The solution b at least includes hydrogen fluoride and cation which atleast include potassium ion (K⁺) and may further include at least oneselected from the group consisting of lithium ion (Li⁺), sodium ion(Na⁺), rubidium ion (Rb⁺), cesium ion (Cs⁺), and ammonium ion (NH₄ ⁺),and may further includes other components as necessary. The solution bis provided as an aqueous solution of hydrofluoric acid which containscation which at least include potassium ion (K⁺) and may further includeat least one selected from the group consisting of lithium ion (Li⁺),sodium ion (Na⁺), rubidium ion (Rb⁺), cesium ion (Cs⁺), and ammonium ion(NH₄ ⁺), and may further includes other components as necessary.Specific examples of potassium ion source which can constitute thesolution b include water-soluble potassium salts such as KF, KHF₂, KOH,KCl, KBr, KI, potassium acetate, and K₂CO₃. Among those, KHF₂ ispreferable, because KHF₂ is soluble without decreasing the concentrationof hydrogen fluoride in the solution, and has a small heat ofdissolution which contributes high safety. Specific examples of thesodium ion source which can constitute the solution b include watersoluble salts such as NaF, NaHF₂, NaOH, NaCl, NaBr, NaI, sodium acetate,and Na₂CO₃. Specific examples of rubidium ion source which canconstitute the solution b include water-soluble rubidium salts such asRbF, rubidium acetate, and Rb₂CO₃. Specific examples of cecium ionsource which can constitute the solution b include water-soluble ceciumsalts such as CsF, cecium acetate, and Cs₂CO₃. Specific examples of theammonium ion source which can constitute the solution b include watersoluble ammonium salts such as NH₄F, ammonia water, NH₄Cl, NH₄Br, NH₄I,ammonium acetate, and (NH₄)₂CO₃F₂. Those SiF₆ sources may be used singlyor in combination of two or more kinds.

The lower-limit value of hydrogen fluoride concentration in the solutionb is generally 20 mass % or greater, preferably 25 mass % or greater,and more preferably 30 mass % or greater. The upper-limit value ofhydrogen fluoride concentration in the solution b is generally 80 mass %or less, preferably 75 mass % or less, more preferably 70 mass % orless. The lower-limit value of hydrogen fluoride concentration in thesolution b is generally 5 mass % or greater, preferably 10 mass % orgreater, and more preferably 15 mass % or greater. The upper-limit valueof cation concentration in the solution b which at least containspotassium ion (K⁺) and may further include at least one selected fromthe group consisting of lithium ion (Li⁺), sodium ion (Na⁺), rubidiumion (Rb⁺), cesium ion (Cs⁺), and ammonium ion (NH₄ ⁺) is generally 80mass % or less, preferably 70 mass % or less, more preferably 60 mass %or less.

The mixing method of the solution a and b is not specifically limited,and the mixing may be performed by adding the solution a into thesolution b while agitating the solution b, or by adding the solution binto the solution a while agitating the solution a. The solution a andthe solution b may be respectively placed in a container and agitated.The first complex ion, the cation which include at least potassium ion(K⁺) and may further include at least one selected from the groupconsisting of lithium ion (Li⁺), sodium ion (Na⁺), rubidium ion (Rb⁺),cesium ion (Cs⁺), and ammonium ion (NH₄ ⁺), and the second complex ionsare reacted in a predetermined ratio by mixing the solution a and thesolution b, to precipitate the crystals of the objective fluoride. Theprecipitated crystal can be collected by solid-liquid separation, e.g.,filtration. The collected crystal may be washed with a solvent such asethanol, isopropyl alcohol, water, or acetone. Further, drying treatmentmay be performed at a temperature generally 50° C. or greater,preferably 55° C. or greater, more preferably 60° C. or greater, andgenerally 110° C. or less, preferably 100° C. or less, and morepreferably 90° C. or less. The drying time is not specifically limitedas long as the water or moisture present on the fluoride fluorescentmaterial can be evaporated, and for example, drying may be performed forabout 10 hours. At the time of mixing of the solution a and the solutionb, considering a difference between the charge composition of thesolution a and the solution b and the composition of the fluorescentmaterial product, the mixing ratio of the solution a and the solution bis appropriately adjusted so that the fluoride fluorescent materialproduct has a desired composition.

The fluoride fluorescent material which has the specific composition canbe manufactured by, for example, a method which includes a step ofmixing a first solution which at least contains a first complex ionwhich includes tetravalent manganese ions and hydrogen fluoride, asecond solution which at least contains cations which at least containpotassium ions (K⁺) and may further contains at least one selected fromthe group consisting of lithium ions (Li⁺), sodium ions (Na⁺), rubidiumions (Rb⁺), cesium ions (Cs⁺), and ammonium ions (NH₄ ⁺), and hydrogenfluoride, and a third solution which at least contains second complexion which contains at least one selected from the group consisting ofGroup 4 elements and Group 14 elements and fluorine ion. Hereinafter,the step may be called as a “second step of manufacturing fluoridefluorescent material”. By mixing the first solution, the secondsolution, and the third solution, a fluoride fluorescent material whichhas a desired composition and a desired weight median diameter can bemanufactured easily and with good productivity.

First Solution

The first solution contains at least first complex ion which includestetravalent manganese ions and hydrogen fluoride, and may contains othercomponents as necessary. The first solution is prepared, for example, asan aqueous solution of hydrofluoric acid which contains tetravalentmanganese source. The manganese source is not specifically limited aslong as it is a chemical compound which contains manganese. Specificexamples of the manganese source which can constitute the first solutioninclude K₂MnF₆, KMnO₄, and K₂MnCl₆. Among those, K₂MnF₆ is preferablebecause it can present stably as MnF₆ complex ions in hydrofluoric acidwhile maintaining its oxidation number (tetravalent) which can serve asan activator. Among the manganese sources, a manganese source which atleast contains cation which include at least K⁺ and may further includeat least one selected from the group consisting of Li⁺, Na⁺, Rb⁺, Cs⁺,and NH₄ ⁺ can also serve as a cation source which at least includes K⁺and may further include at least one selected from the group consistingof Li⁺, Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺, which contained in the secondsolution. For the manganese source which constitutes the first solution,a single manganese source or a combination of two or more manganesesources can be used.

The lower-limit value of hydrogen fluoride concentration in the firstsolution is generally 20 mass % or greater, preferably 25 mass % orgreater, and more preferably 30 mass % or greater. The upper-limit valueof hydrogen fluoride concentration in the first solution is generally 80mass % or less, preferably 75 mass % or less, more preferably 70 mass %or less. With a concentration of hydrogen fluoride 30 mass % or greater,the stability against hydrolysis of the manganese source (e.g. K₂MnF₆)which is a constituent of the first solution can be increased andfluctuation in the tetravalent manganese ion concentration in the firstsolution can be reduced. Accordingly, the amount of manganese activatorcontained in the fluoride fluorescent material thus obtained can becontrolled easily, and the variation (fluctuation) in luminousefficiency in the fluoride fluorescent material tends to be reduced. Inthe case of the hydrogen fluoride concentration being 70 mass % or less,a drop in the boiling point can be prevented and generation of hydrogenfluoride gas can be suppressed. Accordingly, the hydrogen fluorideconcentration in the first solution can be controlled easily, and thevariation or fluctuation in the particle size of the fluoridefluorescent material can be efficiently reduced.

The concentration of the first complex ion in the first solution is notspecifically limited. The lower-limit value of the first complex ionconcentration in the first solution is generally 0.01 mass % or greater,preferably 0.03 mass % or greater, and more preferably 0.05 mass % orgreater. The upper-limit value of the first complex ion concentration inthe first solution is generally 50 mass % or less, preferably 40 mass %or less, and more preferably 30 mass % or less.

Second Solution

The second solution contains cations which at least includes K⁺ and mayfurther include at least one selected from the group consisting of Li⁺,Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺, and hydrogen fluoride, and may furthercontains other components as necessary. The second solution is, forexample, provided as an aqueous solution of hydrofluoric acid whichcontains cations which at least include K⁺ and may further include atleast one selected from the group consisting of Li⁺, Na⁺, Rb⁺, Cs⁺, andNH₄ ⁺. Specific examples of the ion source containing ions which can beconstituent of the second solution include in addition to salts whichcontain potassium such as KF, KHF₂, KOH, KCl, KBr, KI, potassiumacetate, and K₂CO₃, water-soluble salts such as NaF, NaHF₂, NaOH, NaCl,NaBr, NaI, sodium acetate, Na₂CO₃, RbF, rubidium acetate, Rb₂CO₃, CsF,cesium acetate, Cs₂CO₃, NH₄F, ammonia water, NH₄Cl, NH₄Br, NH₄I,ammonium acetate, and (NH₄)₂CO₃. Among those, NaHF₂ is preferable,because NaHF₂ is soluble without decreasing the concentration ofhydrogen fluoride in the solution, and has a small heat of dissolutionwhich contributes high safety. The ion source which constitutes thesecond solution may be used singly or in combination of two or morekinds.

The lower-limit value of hydrogen fluoride concentration in the secondsolution is generally 20 mass % or greater, preferably 25 mass % orgreater, and more preferably 30 mass % or greater. The upper-limit valueof hydrogen fluoride concentration in the second solution is generally80 mass % or less, preferably 75 mass % or less, more preferably 70 mass% or less. The lower-limit value of ion concentration of cations in thesecond solution which at least include K⁺ and may further include atleast one selected from the group consisting of Li⁺, Na⁺, Rb⁺, Cs⁺, andNH₄ ⁺ is generally 5 mass % or greater, preferably 10 mass % or greater,more preferably 15 mass % or greater. The upper-limit value of ionconcentration of cations in the second solution which at least includeK⁺ and may further include at least one selected from the groupconsisting of Li⁺, Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺ is generally 80 mass % orless, preferably 70 mass % or less, more preferably 60 mass % or less.

Third Solution

The third solution contains at least second complex ion which containsat least one selected from Group 4 elements and Group 14 elements inaddition to fluorine ions, and may contain other components asnecessary. The third solution can be provided, for example, an aqueoussolution which contains the second complex ion. The second complex ionpreferably includes at least one selected from the group consisting oftitanium (Ti), zirconium (Zr), hafnium (Hf), silicon (Si), germanium(Ge), and tin (Sn), more preferably includes silicon (Si) or silicon(Si) and germanium (Ge), and further preferably, the second complex ionis a silicon fluoride complex ion.

For example, in the case of the second complex ion contains silicon(Si), the second complex ion source is preferably a chemical compoundwhich contains silicon and fluorine and has high solubility in thesolution. Specific examples of the second complex ion source includeH₂SiF₆, Na₂SiF₆, (NH₄)₂SiF₆, Rb₂SiF₆, and Cs₂SiF₆. Among those, H₂SiF₆is preferable because of its high water-solubility and it's free fromimpurities of alkaline metal elements. The second complex ion sourceswhich constitute the third solution may be used singly or in combinationof two or more kinds.

The lower-limit value of the second complex ion concentration in thethird solution is generally 5 mass % or greater, preferably 10 mass % orgreater, and more preferably 15 mass % or greater. The upper-limit valueof the second complex ion concentration in the third solution isgenerally 80 mass % or less, preferably 70 mass % or less, and morepreferably 60 mass % or less.

The mixing method of the first solution, the second solution, and thethird solution is not specifically limited, and the mixing may beperformed by adding the second solution and the third solution to thefirst solution while agitating the first solution, or by adding thefirst solution and the second solution to the third solution whileagitating the third solution. The first solution, the second solution,and the third solution may be respectively placed in a container andagitationally mixed.

When the first solution, the second solution, and the third solution aremixed, the first complex ion, the cation which include at least K⁺ andmay further includes at least one selected from the group consisting ofLi⁺, Na⁺, Rb⁺, Cs⁺ and NH₄ ⁺ and the second complex ion react at apredetermined ratio and crystals of an intended fluoride having thespecific composition is precipitated. The precipitated crystals can becollected through solid-liquid separation by filtration or the like. Thecrystals may be washed with a solvent such as ethanol, isopropylalcohol, water, or acetone. Further, a drying treatment may be performedat a temperature generally 50° C. or greater, preferably 55° C. orgreater, more preferably 60° C. or greater, and generally 110° C. orless, preferably 100° C. or less, and more preferably 90° C. or less.The drying time is not specifically limited as long as the water ormoisture present on the fluoride crystals is evaporated, and forexample, drying may be performed for about 10 hours.

In mixing of the first solution, the second solution, and the thirdsolution, in consideration of a difference between the chargecomposition of the first to third solutions and the composition of thefluoride to be obtain, it is preferred to appropriately adjust themixing ratio among the first solution, the second solution, and thethird solution so that a fluoride as a product can be obtained with anintended composition.

Second Step

In the second step, a reducing agent is added to the dispersion productcontaining fluoride particles which is obtained in the first step. It ispreferable that the addition of a reducing agent allows for reduction ofat least a portion of tetravalent manganese ions in the first complexions contained in the dispersion product into divalent manganese ions.In the second step, it is preferable that 90 mole % or greater of thefirst complex ion is reduced, and it is more preferable that 95 mole %or greater is reduced.

The reducing agent is not specifically limited as long as it can reducethe first complex ion. More specifically, hydrogen peroxide, oxalicacid, or the like, can be used for the reducing agent. Among those,hydrogen peroxide is preferable in that it has small effect on thefluoride crystals, such as dissolving the fluoride crystals, and it canreduce the first complex ion to water and oxygen in the end, and thus itis easily used in manufacturing processes and the burden on theenvironment is small.

The addition amount of the reducing agent is not specifically limited.The addition amount of the reducing agent can be appropriately selected,for example, according to the content of the first complex ion containedin the dispersion product, but the addition amount which does not affectmuch on the fluctuation of the hydrogen fluoride concentration ispreferable. More specifically, the addition amount of the reducing agentis preferably 3 equivalent % or greater, more specifically 5 equivalent% or greater, with respect to the content of the first complex ioncontained in the dispersion product other than the fluoride crystals. Inthe specification, the term “one equivalent” is referred to the numberof moles of the reducing agent which reduce one mole of the firstcomplex ion to divalent manganese ion.

The second step may include mixing after adding a reducing agent to thedispersion product. The method of mixing the dispersion product and thereducing agent can be appropriately selected from the methods generallyused for mixing, according to the reaction vessel or the like. Thetemperature in the second step is not specifically limited. For example,the reducing agent can be added at a temperature in a range of 15 to 40°C., and preferably in a range of 23 to 28° C. The atmosphere in thesecond step is not specifically limited. The reducing agent can be addedin an atmospheric air, or may be in an inert gas atmosphere such as innitrogen gas. The reaction time in the second step is not specificallylimited. For example, the reaction time may be 1 to 30 minutes, morepreferably 3 to 15 minutes.

Third Step

In the third step, under the presence of hydrogen fluoride, cationswhich include the second complex ions and at least include potassiumions (K⁺), and may further include at least one selected from the groupconsisting of lithium ions (Li⁺), sodium ions (Na⁺), rubidium ions(Rb⁺), cesium ions (Cs⁺), and ammonium ions (NH₄ ⁺), are bring incontact with the fluoride crystals in the dispersion product to whichthe reducing agent has been added, to obtain a fluoride fluorescentmaterial. Under the presence of hydrogen fluoride, the fluoride crystalsare brought in contact with the second complex ion and cations whichinclude the second complex ions and at least include potassium ions(K⁺), and may further include at least one selected from the groupconsisting of lithium ions (Li⁺), sodium ions (Na⁺), rubidium ions(Rb⁺), cesium ions (Cs⁺), and ammonium ions (NH₄ ⁺). Thus, for example,on the surfaces of the fluoride crystals, precipitating a fluoride whichcontains at least one element selected from the group consisting ofGroup 4 elements and Group 14 elements which are contained in the secondcomplex ions, and contains cations which include potassium ions (K⁺) andmay further contain at least one selected from the group consisting oflithium ions (Li⁺), sodium ions (Na⁺), rubidium ions (Rb⁺), cesium ions(Cs⁺), and ammonium ions (NH₄ ⁺), to obtain a desired fluoridefluorescent material.

The third step can be performed separately after the second step, or thethird step can be started after starting and before ending the secondstep so as to perform both the second step and the third step partiallyconcurrently.

In the third step, the fluoride fluorescent material particles areobtained by bringing the fluoride that has the specific composition, forinstance, represented by the formula (I) into contact with the ionswhich include the second complex ion and at least include potassium ion(K⁺), and may further include at least one selected from the groupconsisting of lithium ion (Li⁺), sodium ion (Na⁺), rubidium ion (Rb⁺),cesium ion (Cs⁺), and ammonium ion (NH₄ ⁺). So that it is preferablethat the fluoride fluorescent material has a surface region which has alower tetravalent manganese ion concentration than the tetravalentmanganese ion concentration in the inner region and the surface regionhas a composition represented by the formula (II). In the formula (II),A is at least one selected from the group consisting of alkali metalelements and NH₄ ⁺, or A is a cation which contains at least K⁺ and mayfurther contain at least one selected from the group consisting of Li⁺,Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺, M is at least one element selected from thegroup consisting of Group 4 elements and Group 14 elements, and asatisfies 0<a<b.

A₂[M_(1-a)Mn⁴⁺ _(a)F₆]  (II)

In the formula (II), a and b are not specifically limited as long assatisfying 0<a<b. The value of a can be selected appropriately accordingto the luminous characteristics, the moisture-resistance, and the like,to be obtained. The value of a can be controlled by adjusting thecontact amount of the ions with respect to the fluoride crystals, inwhich the ions include at least potassium ion (K⁺) and may furtherinclude at least one ion selected from the group consisting of lithiumion (Li⁺), sodium ion (Na⁺), rubidium ion (Rb⁺), cesium ion (Cs⁺), andammonium ion (NH₄ ⁺).

In the third step, the method of bringing the fluoride crystals in thedispersion product added with a reducing agent in contact with thecation which include the second complex ions and at least potassium ions(K⁺) and may further include at least one selected from the groupconsisting of lithium ions (Li⁺), sodium ions (Na⁺), rubidium ions(Rb⁺), cesium ions (Cs⁺), and ammonium ions (NH₄ ⁺) is not specificallylimited. Examples of such a method include a preferred method of mixingthe dispersion product added with a reducing agent is brought in contactwith at least one of a solution which contains cations and a solutionwhich contains second complex ions, in which, the solution whichcontains cations at least potassium ions (K⁺) and may further include atleast one selected from the group consisting of lithium ions (Li⁺),sodium ions (Na⁺), rubidium ions (Rb⁺), cesium ions (Cs⁺), and ammoniumions (NH₄ ⁺). In a more preferred method, the dispersion product ismixed with at least one of the second solution and the third solution.In a further preferred method, the dispersion product is mixed with thesecond solution and the third solution. In mixing of the dispersionproduct and either of a solution which contains cations which includesat least potassium ions (K⁺), and may further include at least oneselected from the group consisting of lithium ions (Li⁺), sodium ions(Na⁺), rubidium ions (Rb⁺), cesium ions (Cs⁺), and ammonium ions (NH₄⁺), or a solution which contains the second complex ions, the ions thatare not contained in the solution to use may be contained in thedispersion product respectively in an amount necessary in the thirdstep. The second solution and the third solution in the third step mayhave compositions either similar to or different from that of the secondsolution and the third solution respectively.

In the case where the third step includes mixing of a dispersion productadded with a reducing agent and at least one of a solution whichcontains ions and a solution which contains a second complex ion. Thesolution which contains ions at least includes potassium ions (K⁺) andmay further includes at least one selected from the group consisting oflithium ions (Li⁺), sodium ions (Na⁺), rubidium ions (Rb⁺), cesium ions(Cs⁺), and ammonium ions (NH₄ ⁺). The temperature in the third step isnot specifically limited. For example, the reducing agent can be addedat a temperature in a range of 15 to 40° C., and preferably in a rangeof 23 to 28° C. The atmosphere in the third step is not specificallylimited. The third step can be performed either in ambient atmosphere orin an inert gas atmosphere. The reaction time in the third step is notspecifically limited. For example, the reaction time may be 1 to 60minutes, more preferably 5 to 30 minutes.

In the case where the third step includes mixing the dispersion productadded with a reducing agent and at least one of a solution whichcontains cations and a solution which contain the second complex ion,the addition amount of the solution which contains cations can beselected appropriately according to the luminous characteristics, themoisture-resistance, and the like, to be obtained. The solution whichcontains cations at least includes potassium ions (K⁺) and may furtherincludes at least one selected from the group consisting of lithium ions(Li⁺), sodium ions (Na⁺), rubidium ions (Rb⁺), cesium ions (Cs⁺), andammonium ions (NH₄ ⁺). For example, the addition amount of the secondcomplex ion with respect to the fluoride particles can be 1 mole % to 40mole %, and preferably 5 mole % to 30 mole %.

The surface region of the particles of a fluoride fluorescent materialwhich has the specific composition, for instance, represented by theformula (I) and a surface region which has tetravalent manganese ionconcentration lower than the tetravalent manganese ion concentration inan inner region can be formed after the first step of forming a coreportion, by using a method which includes a variation.

Variation of Second Step

In a variation of second step, the fluoride crystals obtained in thefirst step are placed in an aqueous solution which contains ions of atleast one alkaline earth metal element and a reducing agent. When placedin an aqueous solution which contains alkaline earth metal ions, adissolution reaction of fluoride particles occurs and metal ions andfluorine ions which are constituents of the fluoride particles areformed. The fluorine ions react with the alkaline earth metal ions andan alkaline earth metal fluoride is formed on the surfaces of thefluoride crystals. Thus, a surface region in which the concentration oftetravalent manganese ion is lower than that of the inner region can beformed on the fluoride crystals. The alkaline earth metal fluorideformed on a surface region of the fluoride fluorescent materialparticles can suppress further dissolution reaction of the fluorideparticles. In the presence of a reducing agent, the tetravalentmanganese ions are reduced to divalent manganese ions, so that formationof manganese dioxide can be suppressed. It is considered that theparticles of the fluoride fluorescent material obtained through thevariation of second step have a surface region which contains analkaline earth metal fluoride and also due to the presence of a reducingagent, generation of manganese dioxide on the surfaces of the particlescan be suppressed, so that deterioration in the optical output anddeviation in the chromaticity can be suppressed for a long period. It isconsidered that, thus, good long-term reliability can be achieved.

The solution which contains alkaline earth metal ions at least containsalkaline earth metal ions, counter ions, and water. Examples of thealkaline earth metal ions include magnesium ions (Mg²⁺), calcium ions(Ca²⁺), and strontium ions (Sr²⁺). Among those, in view of reducing thedeviation in the chromaticity and reduction in the optical output, andmoisture-resistance, the alkaline earth metal ions preferably includecalcium ions.

The solution which contains alkaline earth metal ions can be obtained asan aqueous solution of a compound which includes an alkaline earth metalwhich may contain other components (for examples an alcohol such asmethanol or ethanol) as needed. Examples of the compounds which containan alkaline earth metal include nitrate salts of alkaline earth metals(e.g., Mg(NO₃)₂, Ca(NO)₂, Sr(NO₃)₂), acetate salts (e.g., Mg(CH₃CO₂)₂,Ca(CH₃CO₂)₂, Si(CH₃CO₂)₂, chlorides (e.g., MgCl₂, CaCl₂, SrCl₂), iodides(e.g., MgI₂, ClI₂, SrI₂), and bromides (i.e., MgBr₂, CaBr₂, SrBr₂).Those SiF₆ sources may be used singly or in combination of two or morekinds.

The concentration of the alkaline earth metals in the solution whichcontains the alkaline earth metal ions is not specifically limited. Thelower-limit value of the first complex ion concentration in the solutionis generally 0.01 mass % or greater, preferably 0.03 mass % or greater,and more preferably 0.05 mass % or greater. The upper-limit value ofhydrogen fluoride concentration in the solution b is generally 5 mass %or less, preferably 3 mass % or less, more preferably 2 mass % or less.

With respect to 100 parts by mass of the fluoride crystals, the solutionwhich contains an alkaline earth metal ion is preferably 100 to 3000parts by mass, and more preferably 200 to 2000 parts by mass. Themoisture-resistance can be further improved with such a solution whichcontains alkaline earth metal ions.

In the presence of the reducing agent, at least a part of tetravalentmanganese ions generated by a reaction between the fluoride crystals andthe solution which contains alkaline earth metal ions are reduced todivalent manganese ions. More specifically, with the addition of thereducing agent, preferably 90 mole % or greater, more preferably 95 mole% or greater of the tetravalent manganese ions generated by the reactionbetween the fluoride crystals and the solution which contains alkalineearth metal ions are reduced.

The reducing agent is not specifically limited as long as it can reducethe tetravalent manganese ions. More specifically, hydrogen peroxide,oxalic acid, or the like, can be used for the reducing agent. Amongthose, hydrogen peroxide is preferable because hydrogen peroxide canreduce manganese without adversely affecting the base body of thefluoride crystals, such as dissolving the fluoride crystals, andhydrogen peroxide can be broken into harmless water and oxygen, thus,easily handled in the manufacturing steps and has a low impact on theenvironment.

The addition amount of the reducing agent is not specifically limited.The addition amount of the reducing agent can be appropriately selected,for example, according to the content of the manganese contained in thefluoride crystals, but the addition amount which does not affect much onthe base member of the crystals of the fluoride is preferable. Morespecifically, the addition amount of the reducing agent is preferably 1equivalent % or greater, more specifically 3 equivalent % or greater,with respect to the content of the manganese contained in the fluoridecrystals.

In the specification, the term “one equivalent” is referred to thenumber of moles of the reducing agent which reduce one mole of thetetravalent manganese ions to divalent manganese ions.

The lower-limit value of the reducing agent concentration to thesolution which contains alkaline earth metal ions can be for example0.01 mass % or greater, preferably 0.03 mass % or greater, and morepreferably 0.05 mass % or greater. The upper-limit value of the reducingagent concentration to the solution which contains alkaline earth metalions can be for example 5 mass % or less, preferably 3 mass % or less,and more preferably 2 mass % or less.

Contact Method

The method for bringing the fluoride crystals and the solution whichcontains an alkaline earth metal ion is not specifically limited. Forexample, mixing of a solution which contains a reducing agent, thefluoride crystals, and alkaline earth metal ions can be employed.

Contact Time

The contact time of the fluoride crystals and the solution whichcontains alkaline earth metal ions in the presence of a reducing agentis not specifically limited as long as the contact time is sufficient toform the alkaline earth metal fluoride on the surfaces of the fluoridecrystals. For example, the contact time can be 10 minutes to 10 hours,and preferably 30 minutes to 5 hours.

Reaction Temperature

The temperature of mixing the reducing agent, the fluoride crystals andthe solution which contains alkaline earth metal ions is notspecifically limited. For example, the mixing can be performed at atemperature in a range of 15 to 40° C., and preferably in a range of 23to 28° C. The atmosphere of the mixing is not specifically limited. Themixing can be performed either in ambient atmosphere or in an inert gasatmosphere such as in nitrogen gas.

Other Steps

A method of manufacturing a fluoride fluorescent material may furtherinclude providing a fluoride which has a chemical compositionrepresented by the formula (I). The crystals of the fluoride fluorescentmaterial generated in the third step can be collected by solid-liquidseparation, e.g., filtration. The crystals of the fluoride fluorescentmaterial may be washed with a solvent such as ethanol, isopropylalcohol, water, or acetone. Further, drying treatment may be performedat a temperature generally 50° C. or greater, preferably 55° C. orgreater, more preferably 60° C. or greater, and generally 110° C. orless, preferably 100° C. or less, and more preferably 90° C. or less.The drying time is not specifically limited as long as the water ormoisture present on the crystals of the fluorescent material can beevaporated, and for example, drying may be performed for about 10 hours.

Other Fluorescent Materials

The light emitting device preferably includes one or more otherfluorescent materials in addition to the fluoride fluorescent material.Other fluorescent materials can absorb light emitted from a light sourceand converts it to light of different wavelength. Other fluorescentmaterials can be contained in a sealing material as the fluoridefluorescent material described above, and can be a constituent of alight emitting device. For example, at least one selected from the groupconsisting of the below can be preferably used as the other fluorescentmaterials. Such other fluorescent materials include nitride-basedfluorescent materials, oxynitride-based fluorescent materials, andsaialon-based fluorescent materials which are activated mainly with alanthanoid element such as europium, cerium;

alkaline-earth metal halogen apatite fluorescent materials,alkaline-earth metal haloborate fluorescent materials, alkaline-earthmetal aluminate fluorescent materials, alkaline-earth metal silicates,alkaline-earth metal sulfides, alkaline-earth metal thiogallates,alkaline-earth metal silicon nitrides, and germinates, which areactivated mainly with a lanthanoid element such as europium or atransition metal element such as manganese, rare-earth aluminates andrare-earth silicates, which are activated mainly with a lanthanoidelement such as cerium, and organic compounds and organic complexeswhich are activated mainly with a lanthanoid element such as europium.Specific examples of other fluorescent materials include(Ca,Sr,Ba)₂SiO₄:Eu, (Y,Gd)₃(Ga,Al)₅O₁₂:Ce, (Si,Al)₆(O,N)₈:Eu(β-sialon),SrGa₂S₄:Eu, (Ca,Sr)₂Si₅N₈:Eu, CaAlSiN₃:Eu, (Ca,Sr)AlSiN₃:Eu,Lu₃Al₅O₁₂:Ce, and (Ca,Sr,Ba,Zn)₈MgSi₄O₁₆(F,Cl,Br,I)₂:Eu. With otherfluorescent materials, light emitting devices for various color tonescan be provided. In the case where the light emitting device furtherincludes another fluorescent material, the content is not specificallylimited and can be adjusted so that a desired luminous characteristiccan be attained.

In the case of the light emitting device further including one or moreother fluorescent materials, a fluorescent material to emit light ofgreen to yellow light is preferable. More preferably, a fluorescentmaterial which can absorb light in a wavelength range of 380 nm to 485nm and emit light of green to yellow light which has an emission peakwavelength in a range of 495 nm to 590 nm is more preferably contained.The light emitting device includes a fluorescent material which can emitlight of green to yellow color, so that it can be applied more suitablyto liquid crystal display devices.

It is preferable that the fluorescent material to emit light of green toyellow color can be one or more selected from a group consisting of aβ-sialon fluorescent material represented by a composition formula of(Si,Al)₆(O,N)₈:Eu, a thiogallate fluorescent material represented by acomposition formula of SrGa₂S₄:Eu, a halosilicate fluorescent materialrepresented by a composition formula of(Ca,Sr,Ba,Zn)₈MgSi₄O₁₆(F,Cl,Br,I)₂:Eu, or a rare earth aluminatefluorescent material represented by a composition formula(Y,Lu)₃(Al,Ga)₅O₁₂:Ce. Those materials may be used singly or incombination of two or more kinds.

Content of Fluorescent material in Sealing Member

The content of the fluorescent material in the sealing material ispreferably 10 to 200 parts by mass to 100 parts by mass of the binder.With respect to 100 parts by mass of the binder, the fluorescentmaterial is more preferably 20 to 180 parts by mass, further preferably30 to 120 parts by mass, particularly preferably 40 to 100 parts bymass, and most preferably 40 to 80 parts by mass. With the content ofthe fluorescent material in the sealing material being in such a rangedescribed above, the light emitting element can be sufficiently covered,so that the wavelength of the light emitted from the light emittingelement can be efficiently converted by the fluorescent materials andthe light can be efficiently emitted. Further, with the content of thefluorescent material in the sealing material being 10 to 200 parts bymass with respect to 100 parts by mass of the binder, a first portion 9which includes the fluorescent materials 7, 8, which covers the lightemitting element 4 with a uniform thickness, and a second portion 10which has a thickness of one tenth or greater with respect to the entirethickness of the sealing member at directly above the light emittingelement 4 can be formed.

Content of Fluorescent material in First Portion

With respect to 100 parts by mass of the binder, the fluorescentmaterial is more preferably 20 to 400 parts by mass, further preferably25 to 380 parts by mass, particularly preferably 30 to 350 parts bymass, and most preferably 35 to 300 parts by mass. With the content ofthe fluorescent material contained in the first portion being in therange described above, the light emitting element can be covered withthe fluorescent material with a uniform thickness, so that thewavelength of the light emitted from the light emitting element can beefficiently converted by the fluorescent materials.

Mass Ratio of Green-Yellow Fluorescent Material to Red FluorescentMaterial

In the case where the fluorescent material includes a red fluorescentmaterial, that is the fluoride fluorescent material to emit red lightand one or more fluorescent materials to emit green to yellow light, themass ratio of the fluorescent material to emit green to yellow light tothe red fluorescent material (fluorescent material to emit green toyellow light:red fluorescent material) is preferably 5:95 to 95:5, morepreferably 10:90 to 90:10, further preferably 20:80 to 80:20, andparticularly preferably 30:70 to 70:30. In the case where thefluorescent material includes a red fluorescent material and one or morefluorescent materials to emit green to yellow light at a ratio in arange described above, upon absorbing the light from the light emittingelement, a light which has a narrow half-value width of emissionspectrum due to the red fluorescent material containing a fluoride as inthe formula (I), and an emission spectrum of green to yellowfluorescence with a peak which is relatively widely spaced apart fromthe peak of the red fluorescence can be emitted with a wide colorreproduction range and a high luminance.

Filler

The sealing material may contain a filler. The filler is preferably aninorganic filler. Examples of such an inorganic filler include titaniumoxide, zinc oxide, alumina, silica, zirconia, barium titanate, calciumphosphate, calcium carbonate, white carbon, talc, carbonate magnesium,boron nitride, and glass fiber. Among those, the filler is preferablyalumina, silica, or zirconia. The filler may have a shape such as aspherical shape, a scale-like shape, or crushed products of a mass oragglomerates, and of those, a spherical shape is preferable. The fillerpreferably has a volume average particle size (median diameter: d50) of1 μm to 100 μm, measured by using a laser diffraction and scatteringtype particle size distribution measuring device. The filler morepreferably has a volume average particle size (median diameter: d50) of2 μm to 80 μm, further preferably 2 μm to 60 μm, and particularlypreferably 2 μm to 50 μm, measured by using a laser diffraction andscattering type particle size distribution measuring device.

The content of the filler in the sealing material is not specificallylimited. With respect to 100 parts by mass of the binder, the content ofthe filler in the sealing material is preferably 0.1 to 50 parts bymass, more preferably 1 to 30 parts by mass, further preferably 3 to 20parts by mass, and particularly preferably 5 to 15 parts by mass.Containing of a 5 to 15 parts by mass of the filler with respect to 100parts by mass of the binder allows for improving the dispersibility. Forexample, in the case where in addition to the red fluorescent material,one or more fluorescent materials to emit green to yellow light isfurther contained, the red fluorescent material and one or morefluorescent materials to emit green to yellow light can be uniformlydispersed. In the case where a filler is contained in the sealingmaterial, the fluorescent material can be centrifugally sedimented touniformly cover the light emitting element. Thus, the first portion canbe formed. Covering the light emitting element by the first portion in astate in which the fluorescent material to emit green to yellow lightand the red fluorescent material being uniformly dispersed, colordeviation can be improved, the fluorescent material can be efficientlyexcited, and the visible light can be efficiently utilized. The fillermay be contained in the first portion with the fluorescent material, ormay be contained in the second portion.

Nano-Filler

A nano-filler may be contained in the sealing material which is aconstitutive component of the sealing member, before the sealingmaterial is cured. The nano-filler can have a volume average particlesize (median diameter: d50) of the secondary particles of 5 nm to 1000nm, preferably 10 nm to 200 nm, more preferably 20 nm to 180 nm, furtherpreferably 30 μm to 150 μm, particularly preferably 40 μm to 120 μm, andmost preferably 50 nm to 100 nm, measured by using a laser diffractionand scattering type particle size distribution measuring device. For thematerial of the nano-filler, for example, at least one inorganicmaterial selected from the group consisting of inorganic oxides, metalnitrides, metal carbides, carbon compounds, and sulfides. Examples ofsuch inorganic oxides include titanium oxide, tantalum oxide, niobiumoxide, tungsten oxide, zirconium oxide, zinc oxide, indium oxide, tinoxide, hafnium oxide, yttrium oxide, silicon oxide, and aluminum oxide.Also, a composite inorganic oxide of those can be used. Examples ofmetal nitrides include silicon nitride. Examples of metal carbidesinclude silicon carbide. Examples of carbon compounds includelight-transmissive inorganic materials such as diamond or diamond-likecarbons, which are carbon-elemental substances. Examples of sulfidesinclude copper sulfide and tin sulfide. Among those, silicon oxide ispreferable for the material of the nano-filler. The filler may becontained in the first portion with the fluorescent material, or may becontained in the second portion.

The content of nano-filler in the sealing material is not specificallylimited. With respect to 100 parts by mass of the binder, thefluorescent material is preferably 0.1 to 5.0 parts by mass, morepreferably 0.2 to 4.0 parts by mass, further preferably 0.3 to 3.0 partsby mass, and particularly preferably 0.4 to 2.0 parts by mass.Containing of a 0.1 to 5.0 parts by mass of the nano-filler with respectto 100 parts by mass of the binder allows the nano-filler disposedaround the fluorescent material particles. However, it is consideredthat in the case of such a conventional fluoride fluorescent materialactivated with Mn⁴⁺, tetravalent manganese ions which are constituentcomponents of the fluoride fluorescent material and present on thefluorescent material particles may react with atmospheric moisture togenerate manganese dioxide which darkens the surfaces of the particles,resulting in occurrence of deviation in the chromaticity and reductionin the optical output. In the case of containing the nano-filler in thesealing member, the nano-filler can adhere to the circumference of theparticles of the fluoride fluorescent material, so that reaction betweenthe moisture and the tetravalent manganese ions can be furthersuppressed, and thus discoloration of the surfaces of the particles dueto generation of manganese dioxide can be suppressed. Accordingly, inthe light emitting device according to the present disclosure,deterioration in the optical output and deviation in the chromaticitycan be suppressed and more excellent durability can be achieved in along-term reliability test.

Inclusion of a nano-filler in the sealing material allows substantiallyuniform dispersion of the fluorescent material, the filler and thenano-filler when needed, in the binder. Thus, before injecting or at thetime of injecting the sealing material which is to be a sealing member,in the recess of the package, the fluorescent material, and the fillerand the nano-filler as needed, can be injected with a substantiallyuniform amount in the recess of each package. Accordingly, a lightemitting device with little diversion in the color tone among thepackages can be obtained.

Other Materials

The sealing member which is a constitutive component of the sealingmember and before being cured at least includes a binder and afluorescent material, and may include a filler and a nano-filler asneeded. In addition to those, in the case where the binder is made of aresin, a curing agent for hardening the resin may also be contained. Inthe sealing material, a dye, a pigment, or the like may be contained.Voids for dispersing light may be formed in the sealing member to adegree so as not to adversely affect the reliability of the sealingmember.

Method of Manufacturing Sealing Material

The method of manufacturing the sealing material is not specificallylimited and the order of mixing the materials is not also specificallylimited. Examples of the method of manufacturing the sealing materialinclude a method of simultaneously mixing predetermined amount of eachmaterial, and a method of successively mixing predetermined amount ofeach material. The sealing material is preferably manufactured bysuccessively introducing a fluorescent material, if needed a filler, ifneeded a nano-filler, a binder, and other materials in this order into avessel while agitating.

Method of Manufacturing Light Emitting Device

A method of manufacturing a light emitting device includes steps of:providing a package having side walls which define a recess; disposing alight emitting element in the recess; injecting a sealing material inthe recess of the package; sedimenting centrifugally the fluorescentmaterial particles toward a bottom surface in the recess to form asealing member that includes a first sealing member portion and a secondsealing member portion; and curing the binder to form a cured sealingmember.

The sealing material injected in the recess includes particles of afluoride fluorescent material and a binder. The fluorescent materialparticles includes particles of fluoride fluorescent material that havea composition including tetravalent manganese ion, at least oneselecting from the group consisting of alkali metal elements and NH₄ ⁺,and at least one selecting from the group consisting of Group 4 elementsand Group 14 elements. The particles of fluoride fluorescent materialinclude a surface region and an inner region, and both the surfaceregion and the inner region include tetravalent manganese ions. Atetravalent manganese ion concentration of the surface region of theparticles of fluoride fluorescent material is lower than a tetravalentmanganese ion concentration of the inner region of the particles offluoride fluorescent material. The fluoride fluorescent material mayhave a composition represented by the formula (I).

In the centrifuged fluorescent material, the first sealing memberportion covers the light emitting element and includes a first binderportion and the fluorescent material particles located in the firstbinder portion, and the second sealing member portion covers the firstsealing portion and includes a second binder portion and substantiallyno fluorescent material particles located in the second binder portion.

In other words, a method of manufacturing a light emitting elementincludes steps of: providing a package having side walls which define arecess; disposing a light emitting element on bottom of the recess;injecting a sealing material in the recess of the package, the sealingmaterial including particles of a fluoride fluorescent material having achemical composition represented by the following formula (I), and asurface region which has a tetravalent manganese ion concentration lowerthan a tetravalent manganese ion concentration in an inner region of thefluorescent material particles, and a binder; disposing an uncuredsealing member which includes a first portion and a second portion bycentrifugally sedimenting the fluorescent material toward a bottomsurface in the recess to form the first portion which contains thefluorescent material and covers the light emitting element and thesecond portion which substantially does not contain the particles of thefluoride fluorescent material and is located above the first portion;and forming the sealing member by curing the sealing material.

A₂[M_(1-b)Mn⁴⁺ _(b)F₆]  (I)

In the formula (I), A at least one selecting from the group consistingof alkali metal elements and NH₄ ⁺, or A is a cation which contains atleast K⁺ and may further contain at least one selected from the groupconsisting of Li⁺, Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺, M is at least one elementselected from the group consisting of Group 4 elements and Group 14elements, and 0<b<0.2. In the below, a method of manufacturing a lightemitting device will be described with reference to FIG. 1.

Providing Package

A package 3 which has side walls defining a recess 2 is provided.

In the package 3, a first lead 5 and a second lead 6 are integrallyformed as a bottom surface defining the recess 2.

Arranging Light Emitting Element

A light emitting element 4 is disposed and die-bonded on the first lead5 which constitutes the bottom surface of the recess of the package 3.The positive and negative electrodes of the light emitting element 4 arerespectively connected to the first lead 5 and the second lead 6 throughthe corresponding wires 11, 12. A method of manufacturing a lightemitting device according to an embodiment of the invention may includecovering the light emitting element 4, the first lead 5, the second lead6, and the wires 11, 12 with an insulating member. It is preferable thatthe insulating member is made of an inorganic compound disposed in aform of a film (or a layer) disposed on the electrically conductivemember, the wires 11, 12, and the light emitting element 4, by usingsputtering, vapor deposition, or the like. The film (or a layer) of theinsulating member is preferably formed by using atomic layer depositionmethod.

Injecting Sealing Member

Next, in the recess 2 of the package 3, a sealing material which atleast contains a resin and fluorescent materials 7, 8 is injected tofill the recess 2 with the sealing material. The sealing material isinjected in a plurality of recesses 2 in each of a plurality of arrangedpackages 3, preferably by using a syringe or the like. The sealingmaterial may contain a filler, a nano-filler or other materials, asneeded.

Centrifugal Sedimentation of Fluorescent Material

The package 3 with the recess 2 filled with the sealing material issubjected to a centrifugal force so that the particles of the fluoridefluorescent materials 7 and other fluorescent material particles in thesealing material are centrifugally sedimented to cover the lightemitting element 4. Then, with the sealing material, the first portion 9which covers the light emitting element 4 and contains the fluorescentmaterial particles and the second portion 10 which is arranged over thefirst portion 9 and substantially does not contain the fluorescentmaterial particles are formed. The fluorescent material particles arepreferably centrifugally sedimented by placing the package 3 with therecess 2 filled with the sealing material in a magazine and rotating inthe centrifuge device until a sufficient sedimentation is obtained.

The centrifugal sedimentation of the fluorescent material particles isperformed with a direction of a resultant force of a centrifugal forceand gravitational force aligned with a direction perpendicular to thebottom surface of the recess of the package. In the specification, theterm “bottom surface of the package” includes the first lead 5 and thesecond lead 6 on which the light emitting element is mounted. Thecentrifugal sedimentation of the fluorescent material particles isperformed with a direction of a resultant force of a centrifugal forceand gravitational force aligned with a direction perpendicular to thebottom surface of the recess of the package, so that the fluorescentmaterial particles dispersed in the sealing material can be sedimentedwith a substantially uniform thickness on the light emitting element andthe bottom surface of the package, and thus, the first portion 9 with asubstantially uniform thickness can be formed.

It is preferable that the centrifugal sedimentation of the fluorescentmaterial particles is performed so that the thickness of the secondportion is one tenth or greater with respect to the entire thickness ofthe sealing member. Appropriately adjusting the conditions ofcentrifugal sedimentation, the type and amount of the binder in thesealing material, and the type and amount of the fluorescent material,the thickness of the second portion 10 can be adjusted. Centrifugallysedimenting the fluorescent material particles with appropriatelysetting those conditions, the fluorescent material particles can becentrifugally sedimented so that the thickness of the second portion isone tenth or greater with respect to the total thickness of the sealingmaterial.

It is further preferable that the centrifugal sedimentation of thefluorescent material particles is performed so that a thickness of thesecond portion 10 at directly above the light emitting element 4 is onefourth or greater with respect to the total thickness of the sealingmaterial. Appropriately adjusting the conditions of centrifugalsedimentation, the type and amount of the binder in the sealingmaterial, and the type and amount of the fluorescent material, thethickness of the second portion 10 can be adjusted. Centrifugallysedimenting the fluorescent material particles with appropriatelysetting those conditions, the fluorescent material particles can becentrifugally sedimented so that the thickness of the second portion isone fourth or greater with respect to the total thickness of the sealingmaterial.

Curing Sealing Material

After the fluorescent material particles are centrifugally sedimented,the binder is cured. Thus, a light emitting device can be obtained, inwhich a sealing member is formed with the sealing material filled in therecess 2 of the package 3 and has the first portion which contains thefluorescent material and covers the light emitting element and thesecond portion arranged above the first portion and substantially doesnot include the fluorescent material. The method of curing the binder isnot specifically limited and the curing method can be appropriatelyselected according to the type of the binder.

Image Display Device

The image display device has at least one of the light emitting devicedescribed above. An image display device is not specifically limited aslong as manufactured according to a method as described above orincludes a light emitting device and a color filter which are describedabove, and the configuration thereof can be appropriately selected froma conventionally known image display device. The image display devicemay be constituted with, in addition to the light emitting device, acolor filter member and a controlling member for optical transmission,and so forth.

EXAMPLES

The present invention will be described below more specifically withexamples the present invention is not limited by the examples shownbelow.

Manufacturing Example 1 of Fluoride Fluorescent Material

In order to satisfy the charge ratio shown in Table 1, 21.66 g of K₂MnF₆was weighed and dissolved in 800 g of 55 mass % of HF aqueous solution.Then, 400 g of 40 mass % H₂SiF₆ aqueous solution, to obtain the solutionA. Meanwhile, 260.14 g of KHF was weighed, and dissolved in 450 g of a55 mass % HF aqueous solution, to obtain the solution B. Also, 200 g of40 mass % H₂SiF₆ aqueous solution was weighed as the solution C. Next,at room temperature (23 to 28° C.), the solution B and the solution Cwere simultaneously added in drops while agitating the solution A toprecipitate the fluorescent material crystals (fluoride particles), andas shown in Table 2, dropping was temporarily stopped at the time offinishing 75 mass % of dropping of each of the solution B and thesolution C (first step). As the reducing agent, 15 g of 30 mass % H₂O₂aqueous solution was added to the solution A (second step), and then,dropping of the solution B and the solution C was resumed (third step).After finishing the dropping of the solution B and the solution C, theprecipitate was separated and washed with IPA (isopropyl alcohol), anddried at 70° C. for 10 hours to obtain the fluoride fluorescent materialthat has composition of K₂[Si_(0.97)Mn⁴⁺ _(0.03)F₆] of ManufacturingExample 1.

TABLE 1 Solution B Solution C Solution A Charged Amount Charged AmountReducing Charged Amount (g) (g) (g) Agent (g) 40% 55% 55% 40% 30% ChargeComposition H₂SiF₆ HF HF H₂SiF₆ H₂O₂ Ratio (mol) aqueous aqueous aqueousaqueous aqueous K Si Mn F K₂MnF₆ solution solution KHF₂ solutionsolution solution Manufacturing 2 0.95 0.05 6 21.66 400 800 260.14 450200 15 Example 1

TABLE 2 Dropping rate before adding reducing agent (%) Solution BSolution C Manufacturing 75 75 Example 1

Example 1 Manufacturing of Sealing Material

As the red fluorescent material, the fluoride fluorescent materialaccording to the manufacturing example 1 was used. As the fluorescentmaterial to emit green to yellow light, a β-sialon fluorescent materialof (Si,Al)₆(O,N)₈:Eu was used. The fluorescent material to emit green toyellow light and the red fluorescent material are blended at a massratio of the mass of a fluorescent material to emit green to yellowlight with respect to the mass of red fluorescent material to be 27:73.The binder is a resin and a phenyl silicone (Dow Corning (registeredtrademark: OE-6630) was used. For the filler, silica which has a volumeaverage particle size of 11 μm (median diameter: d50), measured by usinga laser diffraction and scattering type particle size distributionmeasuring device (Malvern Master Sizer 2000) was used. For the filler,silicon oxide (AEROSIL (registered trademark)) which has a volumeaverage particle size of secondary particles of 12 nm (median diameter:d50), measured by using a laser diffraction and scattering type particlesize distribution measuring device (Malvern Master Sizer 2000) was used.More specifically, the method can be performed as described below. Inthe sealing material of 100 mass %, the content of the resin can be 91.1mass %. In an agitation vessel, fluorescent materials (red fluorescentmaterial and fluorescent material to emit green to yellow light) areplaced, then, a filler and a nano-filler are placed. As a final, a resinand a hardening agent were placed in the agitation vessel, and agitatedfor about five minutes to obtain the sealing material 1.

Sealing Material

Binder (Main Agent: Silicone Resin) 100 parts by mass. Red fluorescentmaterial (fluoride 31.57 parts by mass (43.25 fluorescent materialaccording to parts by mass × 0.73). manufacturing example 1) Fluorescentmaterial to emit green to 11.68 parts by mass (43.25 yellow light(β-sialon) parts by mass × 0.27) filler (silicon oxide) 5 parts by massnano-filler (silicon oxide: SiO₂) 0.4 parts by mass curing agent (liquidsilicone resin) 400 parts by mass

Method of Manufacturing Light Emitting Device

A package having side walls which define a recess was prepared and alight emitting element was disposed in the recess. Then, a sealingmaterial 1 was injected in the recess of the package by using a syringe.The light emitting element with an emission peak wavelength in a rangeof 380 nm to 485 nm was used. Next, the package 3 with the recess 2filled with the sealing material 1 was placed in a magazine andcentrifugally rotated to centrifugally sedimenting a fluorescentmaterial contained in the sealing material to obtain a first portionwhich contains the fluorescent material and covers the light emittingelement and the second portion located above the first portion andsubstantially does not include the fluorescent material. Before curing,the thickness of the second portion at directly above the light emittingelement was one fourth or greater with respect to the entire thicknessof the sealing member. More specifically, at directly above the lightemitting element, the thickness of the sealing member was 410 μm, thethickness of the first portion was 150 μm, and the thickness of thesecond portion was 260 μm. In the step of centrifugally sedimenting thefluorescent material particles, the direction of the sum of centrifugalforce and gravity was maintained substantially perpendicular to thebottom surface of the recess disposed with the light emitting element.Then, the sealing material was cured to form the first portion whichcontains the fluorescent material and covers the light emitting elementand the second portion located above the first portion and substantiallydoes not include the fluorescent material. Thus, a light emitting deviceof Example 1 was obtained.

FIG. 2 is a diagram showing a 20-power fluorescent microscope image of across section of a light emitting device according to Example 1. Asshown in FIG. 2, the light emitting device 1 of Example 1 is confirmedto have a first portion 9 which contains a fluorescent material andcovers the light emitting element 4, and a second portion 10 locatedabove the first portion 9 and substantially does not contain thefluorescent material.

Comparative Example 1

A light emitting device of Comparative Example 1 was obtained in asimilar manner as in Example 1, except that the fluorescent material inthe sealing material was not subjected to centrifugal sedimentation andthe sealing member which includes the first portion and the secondportion was not formed. In the light emitting device of

Comparative Example 1 The Fluorescent Material was ApproximatelyUniformly Dispersed in the Sealing Member

PCT (Pressure Cooker Test)

Pressure cooker test (PCT) was performed on the light emitting devicesobtained in Example 1 and Comparative Example 1, at 121° C., 100%humidity, and 2 atm. The results are shown in FIGS. 3A to 3D.

As shown in FIG. 3A, the light emitting device obtained in Example 1 ofthe present invention did not show discoloration on the surface of thelight emitting device even after the passage of 200 hours of the PCT. Onthe other hand, as shown in FIG. 3C, discoloration on the surface of thelight emitting device obtained in Comparative Example 1 was confirmedafter 4 hours of the PCT. As shown in FIG. 3C, in the light emittingdevice of Comparative Example 1, discoloration of the surface of thelight emitting device was progressed after 100 hours of PCT, and asshown in FIG. 3D, in the light emitting device of Comparative Example 1,discoloration of the surface of the light emitting device was furtherprogressed after 200 hours of PCT. With the occurrence of discoloration,light is absorbed by the discolored parts which may result in colordeviation and deterioration in the optical output. As the results shownin FIGS. 3A to 3D, good durability of the light emitting device ofExample 1 according to the present invention is confirmed.

Examples 2 to 4, Comparative Examples 2 to 4, and Reference Example

The light emitting devices were fabricated in a similar manner as inExample 1 except for using the red fluorescent materials to emit redlight and the fluorescent materials to emit green to yellow light asshown in Table 3. Also, as a light emitting device of Reference Example,YAG is used as the fluorescent material. Each of the light emittingdevices of Reference Example, Examples 2 to 4, and Comparative Examples2 to 4 has a sealing member which includes a first portion whichcontains one or more fluorescent materials and covers the light emittingelement and a second portion arranged above the first portion andsubstantially does not contain a fluorescent material.

NTSC Ratio

The light emitting devices obtained in Reference Example, Examples 2 to4, and Comparative Examples 2 to 4 were respectively assembled in imagedisplay devices. The NTSC ratio of each image display device wasmeasured. The NTSC ratio is the ratio of the area of a triangle definedby three chromaticity points red, green, blue of the display apparatusto be evaluated to the area of a triangle defined by the chromaticitypoints of three primary colors, red (0.670, 0.330), green (0.210, 0.710)and blue (0.140, 0.080), of the standard chromaticity (x, y) accordingto the CIE 1931 XYZ display color system established by the NationalTelevision Standards Committee of the USA. The area ratio describedabove is defined as a color reproduction range and it is determined thehigher the ratio the higher is the color reproductivity. It ispreferable that an image display device satisfies a color reproductionrange of a NTSC ratio being 70% or greater, on the CIE 1931 chromaticitydiagram.

sRGB

The light emitting devices obtained in Reference Example, Examples 2 to4, and Comparative Examples 2 to 4 were respectively assembled in imagedisplay devices. The sRGB ratio of each image display device wasmeasured. The sRGB ratio is the ratio of the area of a triangle definedby three chromaticity points red, green, blue of the display apparatusto be evaluated to the area of a triangle defined by the chromaticitypoints of three primary colors, red (0.640, 0.330), green (0.300, 0.600)and blue (0.150, 0.060), of the standard chromaticity (x, y) accordingto the CIE 1931 XYZ display color system established by theInternational Electrotechnical Commission. The area ratio describedabove is defined as a color reproduction range and it is determined thehigher the ratio the higher is the color reproductivity.

Relative Luminous Flux of LED

Luminous flux of the light emitting devices obtained in ReferenceExample, Examples 2 to 4, and Comparative Examples 2 to 4 wasrespectively measured by integrating sphere and relative luminous fluxwas calculated based on luminous flux of Reference Example.

The measurement results of the NTSC ratio, the sRGB, and the relativeluminous flux of the light emitting devices obtained in ReferenceExample, Examples 2 to 4, and Comparative Examples 2 to 4 are shown inTable 3. In Table 3, the values in parentheses shown under eachfluorescent material indicates the maximum wavelength in the emissionspectrum of each fluorescent material.

TABLE 3 Fluorescent material Relative Green Red luminous fluorescentfluorescent sRGB flux material material NTSC (U‘V’Area) of LED ReferenceYAG 70% 100% 100 Example Example 2 β-sialon Manufacturing 90% 135% 87(540 nm) Example 1 (630 nm) Example 3 β-sialon Manufacturing 93% 137% 82(535 nm) Example 1 (630 nm) Example 4 β-sialon Manufacturing 96% 139% 75(531 nm) Example 1 (630 nm) Comparative β-sialon CASN 77% 123% 68Example 1 (540 nm) (660 nm) Comparative β-sialon CASN 80% 127% 64Example 2 (535 nm) (660 nm) Comparative β-sialon CASN 83% 130% 58Example 3 (531 nm) (660 nm)

As shown in Table 3, the light emitting devices of Examples 2 to 4 withthe fluorescent material of Manufacturing Example 1 exhibit all the NTSCratio, the sRGB, and the relative luminous flux (LED) superior to thoseobtained by the light emitting devices of Comparative Examples 2 to 4with the fluorescent materials other than the fluorescent material ofManufacturing Example 1, and exhibit an improvement in both the colorreproductivity and the relative luminous flux. Compared to the relativeluminous flux 100 of the light emitting device of Reference Example, therelative luminous fluxes of the light emitting devices of ComparativeExamples 2 to 4 showed lower values of 58, 64, 68, respectively, but therelative luminous fluxes of the light emitting devices of Examples 2 to4 showed improved values of 87, 82, and 75, compared to that ofComparative Examples 2 to 4.

In the light emitting device according to the present disclosure,deterioration in the optical output and color deviation are suppressed.Thus, the light emitting device according to the present disclosure canbe advantageously used particularly for light sources of white lightingwhich use blue light emitting diodes as their light source, backlightlight sources, LED displays, signals, pilot light switches, varioussensors, and various indicators, and particularly, in lightingapplications, exhibits superior durability and luminous characteristics.

It is to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

All publications, patent applications, and technical standards mentionedin this specification are herein incorporated by reference to the sameextent as if each individual publication, patent application, ortechnical standard was specifically and individually indicated to beincorporated by reference.

What is claimed is:
 1. A method of manufacturing a light emitting devicecomprising: providing a package having side walls which define a recess;disposing a light emitting element in the recess; injecting a sealingmaterial in the recess of the package, the sealing material includingfluorescent material particles and a binder, the fluorescent materialparticles including particles of fluoride fluorescent material that havea composition including tetravalent manganese ions, at least oneselecting from the group consisting of alkali metal elements and NH₄ ⁺and at least one selecting from the group consisting of Group 4 elementsand Group 14 elements; sedimenting centrifugally the fluorescentmaterial particles toward a bottom surface in the recess to form asealing member that comprises a first sealing member portion and asecond sealing member portion, the first sealing member portion coveringthe light emitting element, and comprising a first binder portion andthe fluorescent material particles located in the first binder portion,and the second sealing member portion covering the first sealingportion, and comprising a second binder portion and substantially nofluorescent material particles located in the second binder portion; andcuring the binder to form a cured sealing member, wherein the particlesof fluoride fluorescent material include a surface region and an innerregion, both the surface region and the inner region comprisingtetravalent manganese ions, and wherein a tetravalent manganese ionconcentration of the surface region of the particles of fluoridefluorescent material is lower than a tetravalent manganese ionconcentration of the inner region of the particles of fluoridefluorescent material.
 2. The method according to claim 1, whereinsedimenting centrifugally the fluorescent material particles isperformed with a direction of a resultant force of a centrifugal forceand gravitational force is aligned with a direction perpendicular to abottom surface of the recess of the package.
 3. The method according toclaim 1, wherein sedimenting centrifugally the fluorescent materialparticles is performed so that a thickness of the second portion atdirectly above the light emitting element is one tenth or greater withrespect to an entire thickness of the sealing material.
 4. The methodaccording to claim 2, wherein sedimenting centrifugally the fluorescentmaterial particles is performed so that a thickness of the secondportion at directly above the light emitting element is one tenth orgreater with respect to an entire thickness of the sealing material. 5.The method according to claim 1, wherein sedimenting centrifugally thefluorescent material particles is performed so that a thickness of thesecond portion at directly above the light emitting element is onefourth or greater with respect to an entire thickness of the sealingmaterial.
 6. The method according to claim 2, wherein sedimentingcentrifugally the fluorescent material particles is performed so that athickness of the second portion at directly above the light emittingelement is one fourth or greater with respect to an entire thickness ofthe sealing material.
 7. The method according to claim 1, wherein theparticles of fluoride fluorescent material have a compositionrepresented by the following formula (I),A₂[M_(1-b)Mn⁴⁺ _(b)F₆]  (I) wherein A is at least one selected from thegroup consisting of alkali metal elements and NH₄ ⁺, M is at least oneselecting from the group consisting of Group 4 elements and Group 14elements, and 0<b<0.2.
 8. The method according to claim 7, wherein thesurface region of the particles of fluoride fluorescent material has acomposition represented by the following formula (II),A₂[M_(1-a)Mn⁴⁺ _(a)F₆]  (II) wherein A is at least one selected from thegroup consisting of alkali metal elements and NH₄ ⁺, M is at least oneselecting from the group consisting of Group 4 elements and Group 14elements, and 0<a<b.
 9. The method according to claim 2, wherein theparticles of fluoride fluorescent material have a compositionrepresented by the following formula (I),A₂[M_(1-b)Mn⁴⁺ _(b)F₆]  (I) wherein A is at least one selected from thegroup consisting of alkali metal elements and NH₄ ⁺, M is at least oneselecting from the group consisting of Group 4 elements and Group 14elements, and 0<b<0.2.
 10. The method according to claim 9, wherein thesurface region of the particles of fluoride fluorescent material has acomposition represented by the following formula (II),A₂[M_(1-a)Mn⁴⁺ _(a)F₆]  (II) wherein A is at least one selected from thegroup consisting of alkali metal elements and NH₄ ⁺, M is at least oneselecting from the group consisting of Group 4 elements and Group 14elements, and 0<a<b.
 11. The method according to claim 3, wherein theparticles of fluoride fluorescent material have a compositionrepresented by the following formula (I),A₂[M_(1-b)Mn⁴⁺ _(b)F₆]  (I) wherein A is at least one selected from thegroup consisting of alkali metal elements and NH₄ ⁺, M is at least oneselecting from the group consisting of Group 4 elements and Group 14elements, and 0<b<0.2.
 12. The method according to claim 11, wherein thesurface region of the particles of fluoride fluorescent material has acomposition represented by the following formula (II),A₂[M_(1-a)Mn⁴⁺ _(a)F₆]  (II) wherein A is at least one selected from thegroup consisting of alkali metal elements and NH₄ ⁺, M is at least oneselecting from the group consisting of Group 4 elements and Group 14elements, and 0<a<b.